diff --git a/README.md b/README.md
index a78b793ca..05c727a7a 100644
--- a/README.md
+++ b/README.md
@@ -68,6 +68,17 @@ benilla builds and runs on macOS, Linux and Windows. You need:
   Xcode command line tools, on Linux the ALSA and udev development packages and pkg-config, on
   Windows the MSVC build tools that the Rust installer sets up.
 
+This fork also reads community **ruRU language packs for 1.12.1** from `Data/ruRU`.
+Keep the base MPQs in `Data` and the Russian `patch-*.MPQ` files in that subfolder;
+`WOW_DATA` points to `Data`, not to `ruRU`. An installed pack selects Russian automatically.
+`WOW_LOCALE=ruRU` requires the pack, `WOW_LOCALE=enUS` selects the English base chain, and
+`WOW_LOCALE=auto` restores automatic selection. Restart the client after changing the language.
+The selected chain supplies DBC names, interface strings, fonts, textures and audio; missing
+localized files fall back to the base chain. Benilla's own settings and menu captions also have
+Russian translations. The login sends the selected locale to the server; server-supplied quest,
+NPC and item text requires translations on that server. Packs for later expansions are unsupported.
+`moonwell-deploy stage` preserves an installed `ruRU` archive folder in the distribution.
+
 ```sh
 WOW_DATA=/path/to/WoW/Data cargo run --release -p benilla
 ```
diff --git a/crates/benilla-app/assets/ui/GameMenuAdapters.xml b/crates/benilla-app/assets/ui/GameMenuAdapters.xml
index 43cf5fea8..80a0405c4 100644
--- a/crates/benilla-app/assets/ui/GameMenuAdapters.xml
+++ b/crates/benilla-app/assets/ui/GameMenuAdapters.xml
@@ -39,7 +39,7 @@
         -- space: a width or height of 0 is no size in 1.12's layout, not a flat rect.
 
         -- Literal: 1.12 has no GAMEMENU_OPTIONS; its OPTIONS_MENU is "Options Menu".
-        GameMenuButtonOptions:SetText("Options")
+        GameMenuButtonOptions:SetText(BenillaUiText("Options"))
         GameMenuButtonOptions:ClearAllPoints()
         GameMenuButtonOptions:SetPoint("TOP", GameMenuFrame, "TOP", 0, -32)
         GameMenuButtonOptions:SetScript("OnClick", function()
@@ -66,12 +66,12 @@
         local editMode = CreateFrame("Button", "BenillaGameMenuButtonEditMode", GameMenuFrame,
             "GameMenuButtonTemplate")
         editMode:SetPoint("TOP", GameMenuButtonKeybindings, "TOP", 0, -19)
-        editMode:SetText("Edit Mode")
+        editMode:SetText(BenillaUiText("Edit Mode"))
         editMode:Disable()
         local support = CreateFrame("Button", "BenillaGameMenuButtonSupport", GameMenuFrame,
             "GameMenuButtonTemplate")
         support:SetPoint("TOP", editMode, "BOTTOM", 0, 0)
-        support:SetText("Support")
+        support:SetText(BenillaUiText("Support"))
         support:Disable()
 
         GameMenuButtonMacros:SetPoint("TOP", support, "BOTTOM", 0, 0)
diff --git a/crates/benilla-app/assets/ui/KeyBindingsPage.xml b/crates/benilla-app/assets/ui/KeyBindingsPage.xml
index 03d4de7ee..7cb1e7e9a 100644
--- a/crates/benilla-app/assets/ui/KeyBindingsPage.xml
+++ b/crates/benilla-app/assets/ui/KeyBindingsPage.xml
@@ -471,7 +471,7 @@
         }
         -- Reset To Default confirms, as the era's does; our string, since 1.12 has none.
         StaticPopupDialogs["BENILLA_CONFIRM_RESET_KEYBINDINGS"] = {
-            text = "Are you sure you want to reset all keybindings to their defaults?",
+            text = BenillaUiText("Are you sure you want to reset all keybindings to their defaults?"),
             button1 = BenillaKeyBindings_String("OKAY", "Okay"),
             button2 = BenillaKeyBindings_String("CANCEL", "Cancel"),
             OnAccept = function()
@@ -491,7 +491,7 @@
             for i = 1, GetNumBindings() do
                 local command = GetBinding(i)
                 if not BenillaKeyBindings_IsHeader(command) then
-                    local tag = string.upper(BenillaKeyBindings_String("BINDING_NAME_" .. command, command))
+                    local tag = BenillaUiUpper(BenillaKeyBindings_String("BINDING_NAME_" .. command, command))
                     local s = BenillaOptionsSearch_Score(tag, words)
                     if s then
                         table.insert(out, { score = s, index = i })
diff --git a/crates/benilla-app/assets/ui/OptionsFrame.xml b/crates/benilla-app/assets/ui/OptionsFrame.xml
index 9b425483a..d97b4d18e 100644
--- a/crates/benilla-app/assets/ui/OptionsFrame.xml
+++ b/crates/benilla-app/assets/ui/OptionsFrame.xml
@@ -118,6 +118,7 @@
 
         -- The wash at the era atlas size, in the 1.14 hover steel-blue.
         function BenillaOptionsCategoryRow_OnLoad(row, key, label)
+            label = BenillaUiText(label)
             row.categoryKey = key
             row.pageTitle = label
             row:SetText(label)
@@ -180,7 +181,7 @@
         -- Results are the live rows, so writes work mid-search.
 
         function BenillaOptionsSearch_Words(text)
-            local up = string.upper(text)
+            local up = BenillaUiUpper(text)
             local words = { up }
             for w in string.gfind(up, "([^, ]+)") do
                 table.insert(words, w)
@@ -324,7 +325,7 @@
             BenillaKeyBindingsPage.searchPainted = nil
             BenillaKeyBindings_SetSelected(nil)
             BenillaOptionsFrameContainerUnbind:Hide()
-            BenillaOptionsFrameContainerTitle:SetText("Search Results")
+            BenillaOptionsFrameContainerTitle:SetText(BenillaUiText("Search Results"))
             BenillaOptionsFrameContainerDefaults:Hide()
 
             local order, groups = BenillaOptionsSearch_FindMatches(text)
@@ -434,6 +435,24 @@
             .. "which it could only do in exclusive fullscreen. benilla applies it to the "
             .. "finished image instead, so it works in both display modes."
 
+        if GetLocale() == "ruRU" then
+            BENILLA_TOOLTIP_RENDER_SCALE =
+                "Меняет разрешение трёхмерного мира относительно размера окна. Интерфейс не меняется.\n\n"
+                .. "Значения ниже 100% повышают частоту кадров, но снижают чёткость. "
+                .. "Значения выше 100% сглаживают края за счёт производительности. "
+                .. "Изменение вступает в силу после нажатия кнопки «Применить»."
+            BENILLA_TOOLTIP_BACKGROUND_SOUND =
+                "Продолжает воспроизведение звука игры, когда активно другое окно.\n\n"
+                .. "Если выключено, при переключении в другое окно игра становится беззвучной. "
+                .. "Звуки при этом продолжают идти и могут закончиться до вашего возвращения."
+            BENILLA_TOOLTIP_DISPLAY_MODE =
+                "Оконный режим на весь экран использует окно без рамки. Обычный оконный режим "
+                .. "оставляет рамку и заголовок окна.\n\nЭксклюзивный полноэкранный режим не используется."
+            BENILLA_TOOLTIP_BRIGHTNESS =
+                "Делает изображение светлее или темнее, в том числе ночью, в пещерах и помещениях.\n\n"
+                .. "Коррекция применяется к готовому изображению и работает в обоих режимах экрана."
+        end
+
         BENILLA_OPTIONS_PAGE_ROWS = {
             -- The era Controls order first; the rest follow their 1.12 box's columns.
             Controls = {
@@ -493,9 +512,10 @@
 
         -- `tip` is a GlobalStrings key, resolved at hover as UIOptionsFrame.lua:265 does.
         function BenillaOptionsRow_OnLoad(row, cvar, label, tip, child)
+            label = BenillaUiText(label)
             row.cvar = cvar
             row.tip = tip
-            row.searchTag = string.upper(label)
+            row.searchTag = BenillaUiUpper(label)
             -- BenillaOptionsRow_SetEnabled's disabled font must keep the child size.
             row.child = child
             local l = getglobal(row:GetName() .. "Label")
@@ -633,7 +653,7 @@
             local row = dd:GetParent()
             for _, e in ipairs(row.entries) do
                 local info = {}
-                info.text = e.text
+                info.text = BenillaUiText(e.text)
                 info.value = e.value
                 info.func = BenillaOptionsDropdownEntry_OnClick
                 UIDropDownMenu_AddButton(info)
@@ -670,7 +690,7 @@
             end
             if match then
                 dd.selectedValue = match.value
-                UIDropDownMenu_SetText(match.text, dd)
+                UIDropDownMenu_SetText(BenillaUiText(match.text), dd)
                 -- As UIOptionsFrameCameraDropDown_OnClick retargets OPTION_TOOLTIP_CAMERA<id>.
                 if match.tip then row.tip = match.tip end
             else
@@ -3075,6 +3095,7 @@
                  wheel stay off until a capsule is selected (BenillaKeyBindings_SetSelected). -->
             <OnLoad>
                 this:EnableKeyboard(false)
+                BenillaUiLocalize(this)
                 this:EnableMouseWheel(false)
             </OnLoad>
             <OnKeyDown>BenillaKeyBindings_OnKeyDown()</OnKeyDown>
diff --git a/crates/benilla-app/assets/ui/ScriptLogFrame.xml b/crates/benilla-app/assets/ui/ScriptLogFrame.xml
index 13fd9dcc0..b0542f773 100644
--- a/crates/benilla-app/assets/ui/ScriptLogFrame.xml
+++ b/crates/benilla-app/assets/ui/ScriptLogFrame.xml
@@ -78,13 +78,13 @@
 
             local summary
             if total == 0 then
-                summary = "No problems this session."
+                summary = BenillaUiText("No problems this session.")
             elseif total > shown then
-                summary = format("%d problems (%d older not kept)", total, total - shown)
+                summary = format(BenillaUiText("%d problems (%d older not kept)"), total, total - shown)
             elseif total == 1 then
-                summary = "1 problem"
+                summary = BenillaUiText("1 problem")
             else
-                summary = format("%d problems", total)
+                summary = format(BenillaUiText("%d problems"), total)
             end
             getglobal("BenillaScriptLogSummary"):SetText(summary)
 
@@ -370,7 +370,7 @@
             </Button>
         </Frames>
         <Scripts>
-            <OnLoad>BenillaScriptLogFrame_OnLoad()</OnLoad>
+            <OnLoad>BenillaUiLocalize(this); BenillaScriptLogFrame_OnLoad()</OnLoad>
             <!-- A spin bubbles up the parent chain; the detail pane's own handler wins there. -->
             <OnMouseWheel>BenillaScriptLogFrame_OnMouseWheel(arg1)</OnMouseWheel>
             <OnShow>BenillaScriptLog_Update()</OnShow>
diff --git a/crates/benilla-app/assets/ui/ScrollTemplates.xml b/crates/benilla-app/assets/ui/ScrollTemplates.xml
index 19a3f3e8a..7ad383fd2 100644
--- a/crates/benilla-app/assets/ui/ScrollTemplates.xml
+++ b/crates/benilla-app/assets/ui/ScrollTemplates.xml
@@ -7,6 +7,127 @@
         because the loader runs every `<Scripts>` block in order.
     -->
     <Script><![CDATA[
+        -- Shared captions for our layer: stock labels resolve from the installed GlobalStrings;
+        -- only captions authored by benilla have translations here.
+        local benillaLabelKeys = {
+            ["Action Bars"] = "ACTIONBAR_LABEL", ["Ambience Volume"] = "AMBIENCE_VOLUME",
+            ["Attack on assist"] = "ASSIST_ATTACK", ["Auto Clear AFK"] = "CLEAR_AFK",
+            ["Auto Self Cast"] = "AUTO_SELF_CAST_TEXT", ["Auto-Follow Speed"] = "AUTO_FOLLOW_SPEED",
+            ["Block Trades"] = "BLOCK_TRADES", ["Brightness"] = "OPTIONS_BRIGHTNESS", ["Chat"] = "CHAT_LABEL",
+            ["Click-to-Move"] = "CLICK_TO_MOVE", ["Close"] = "CLOSE",
+            ["Controls"] = "CONTROLS_LABEL", ["Defaults"] = "DEFAULTS",
+            ["Disable Spam Filter"] = "DISABLE_SPAM_FILTER", ["Enable All Sound"] = "ENABLE_ALL_SOUND",
+            ["Enable Ambience"] = "ENABLE_AMBIENCE", ["Enable Error Speech"] = "ENABLE_ERROR_SPEECH",
+            ["Enable Music"] = "ENABLE_MUSIC", ["Enhanced Tooltips"] = "USE_UBERTOOLTIPS",
+            ["Environment Detail"] = "ENVIRONMENT_DETAIL", ["Follow Terrain"] = "FOLLOW_TERRAIN",
+            ["Head Bob"] = "HEAD_BOB", ["Invert Mouse"] = "INVERT_MOUSE",
+            ["Keybindings"] = "KEY_BINDINGS", ["Master Volume"] = "MASTER_VOLUME",
+            ["Mouse Look Speed"] = "MOUSE_LOOK_SPEED", ["Mouse Sensitivity"] = "MOUSE_SENSITIVITY",
+            ["Music Volume"] = "MUSIC_VOLUME", ["NPC Names"] = "SHOW_NPC_NAMES",
+            ["Periodic Damage"] = "LOG_PERIODIC_EFFECTS", ["Pet Damage"] = "SHOW_PET_MELEE_DAMAGE",
+            ["Player Guild Names"] = "SHOW_GUILD_NAMES", ["Player Names"] = "SHOW_PLAYER_NAMES",
+            ["Player Titles"] = "SHOW_PLAYER_TITLES", ["Profanity Filter"] = "PROFANITY_FILTER",
+            ["Search"] = "SEARCH", ["Show Own Name"] = "SHOW_OWN_NAME",
+            ["Show Target Damage"] = "SHOW_DAMAGE_TEXT", ["Smart Pivot"] = "SMART_PIVOT",
+            ["Sound Volume"] = "SOUND_VOLUME", ["Sticky Targeting"] = "GAMEFIELD_DESELECT_TEXT",
+            ["Terrain Distance"] = "FARCLIP", ["UI Scale"] = "UI_SCALE",
+            ["Vertical Sync"] = "VERTICAL_SYNC", ["Water Collision"] = "WATER_COLLISION",
+            ["Weather Intensity"] = "WEATHER_DETAIL",
+            ["Smart"] = "CAMERA_SMART", ["Always"] = "ALWAYS", ["Never"] = "CAMERA_NEVER",
+            ["Raid"] = "RAID", ["Party"] = "PARTY", ["Solo"] = "SOLO",
+            ["Scroll Up"] = "COMBAT_TEXT_SCROLL_UP", ["Scroll Down"] = "COMBAT_TEXT_SCROLL_DOWN",
+            ["Arc"] = "COMBAT_TEXT_SCROLL_ARC",
+            ["Always Show ActionBars"] = "ALWAYS_SHOW_MULTIBARS_TEXT",
+            ["Automatic Quest Tracking"] = "AUTO_QUEST_WATCH_TEXT",
+            ["Buff Durations"] = "SHOW_BUFF_DURATION_TEXT",
+            ["Camera Following Style"] = "CAMERA_FOLLOWING_STYLE",
+            ["Combat Text Float Mode"] = "COMBAT_TEXT_FLOAT_MODE_LABEL",
+            ["Detailed Loot Information"] = "SHOW_LOOT_SPAM",
+            ["Enable Floating Combat Text"] = "SHOW_COMBAT_TEXT_TEXT",
+            ["Guild Member Alert"] = "GUILDMEMBER_ALERT",
+            ["Instant Quest Text"] = "SHOW_QUEST_FADING_TEXT",
+            ["Lock ActionBars"] = "LOCK_ACTIONBAR_TEXT", ["Max Camera Distance"] = "MAX_FOLLOW_DIST",
+            ["Remove Chat Hover Delay"] = "REMOVE_CHAT_DELAY_TEXT",
+            ["Show Auras"] = "COMBAT_TEXT_SHOW_AURAS_TEXT",
+            ["Show Chat Bubbles"] = "CHAT_BUBBLES_TEXT",
+            ["Show Combat State"] = "COMBAT_TEXT_SHOW_COMBAT_STATE_TEXT",
+            ["Show Combo Points"] = "COMBAT_TEXT_SHOW_COMBO_POINTS_TEXT",
+            ["Show Damage Reduction"] = "COMBAT_TEXT_SHOW_RESISTANCES_TEXT",
+            ["Show Detailed Tooltips"] = "SHOW_NEWBIE_TIPS_TEXT",
+            ["Show Dodge/Parries/Misses"] = "COMBAT_TEXT_SHOW_DODGE_PARRY_MISS_TEXT",
+            ["Show Energy Gains"] = "COMBAT_TEXT_SHOW_MANA_TEXT",
+            ["Show Fading Auras"] = "COMBAT_TEXT_SHOW_AURA_FADE_TEXT",
+            ["Show Friendly Healer Names"] = "COMBAT_TEXT_SHOW_FRIENDLY_NAMES_TEXT",
+            ["Show Honor Gained"] = "COMBAT_TEXT_SHOW_HONOR_GAINED_TEXT",
+            ["Show Loading Screen Tips"] = "SHOW_TIPOFTHEDAY_TEXT",
+            ["Show Low Mana and Health"] = "COMBAT_TEXT_SHOW_LOW_HEALTH_MANA_TEXT",
+            ["Show Party Chat Bubbles"] = "PARTY_CHAT_BUBBLES_TEXT",
+            ["Show Reactive Spells and Abilities"] = "COMBAT_TEXT_SHOW_REACTIVES_TEXT",
+            ["Show Reputation"] = "COMBAT_TEXT_SHOW_REPUTATION_TEXT",
+            ["Show Target of Target"] = "SHOW_TARGET_OF_TARGET_TEXT", ["Status Bar Text"] = "STATUS_BAR_TEXT",
+            ["Show Bottom Left ActionBar"] = "SHOW_MULTIBAR1_TEXT",
+            ["Show Bottom Right ActionBar"] = "SHOW_MULTIBAR2_TEXT",
+            ["Show Right ActionBar"] = "SHOW_MULTIBAR3_TEXT", ["Show Right ActionBar 2"] = "SHOW_MULTIBAR4_TEXT",
+            ["Show Cloak"] = "SHOW_CLOAK", ["Show Helm"] = "SHOW_HELM", ["Show Tutorials"] = "SHOW_TUTORIALS",
+        }
+        local benillaRussianLabels = {
+            ["Options"] = "Настройки", ["Game"] = "Игра", ["AddOns"] = "Аддоны",
+            ["Gameplay"] = "Игровой процесс", ["System"] = "Система",
+            ["Interface"] = "Интерфейс", ["Combat"] = "Бой", ["Graphics"] = "Графика",
+            ["Audio"] = "Звук", ["Nameplates"] = "Индикаторы здоровья",
+            ["Search Results"] = "Результаты поиска", ["No results found."] = "Ничего не найдено.",
+            ["Apply"] = "Применить", ["Auto Loot"] = "Автосбор добычи",
+            ["Display Mode"] = "Режим экрана", ["Render Scale"] = "Масштаб рендеринга",
+            ["Windowed"] = "Оконный", ["Windowed (Fullscreen)"] = "Оконный (на весь экран)",
+            ["Party or Raid"] = "Группа или рейд",
+            ["Enable Sound in Background"] = "Звук в фоне", ["Show When"] = "Показывать",
+            ["Enemy Name Plates"] = "Индикаторы врагов", ["Friendly Name Plates"] = "Индикаторы союзников",
+            ["On"] = "Вкл.", ["Off"] = "Выкл.",
+            ["Are you sure you want to reset all keybindings to their defaults?"] =
+                "Сбросить все назначения клавиш к значениям по умолчанию?",
+            ["Edit Mode"] = "Режим редактирования", ["Support"] = "Поддержка",
+            ["Script Errors"] = "Ошибки скриптов", ["Clear"] = "Очистить",
+            ["No problems this session."] = "В этом сеансе ошибок нет.",
+            ["1 problem"] = "Одна ошибка", ["%d problems"] = "Ошибок: %d",
+            ["%d problems (%d older not kept)"] = "Ошибок: %d (старых не сохранено: %d)",
+        }
+        function BenillaUiText(text)
+            if GetLocale() ~= "ruRU" then return text end
+            local key = benillaLabelKeys[text]
+            return (key and getglobal(key)) or benillaRussianLabels[text] or text
+        end
+
+        -- Lua's byte-wise upper leaves UTF-8 Cyrillic unchanged. Both the labels and the query
+        -- use this fold, so the options search matches Russian regardless of letter case.
+        function BenillaUiUpper(text)
+            local result = string.upper(text)
+            if GetLocale() == "ruRU" then
+                local lower = "абвгдеёжзийклмнопрстуфхцчшщъыьэюя"
+                local upper = "АБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯ"
+                for i = 1, string.len(lower), 2 do
+                    result = string.gsub(result, string.sub(lower, i, i + 1), string.sub(upper, i, i + 1))
+                end
+            end
+            return result
+        end
+
+        -- Called at creation, after the children exist, for static captions owned by our windows.
+        function BenillaUiLocalize(frame)
+            if GetLocale() ~= "ruRU" then return end
+            local function caption(object)
+                if object.GetText and object.SetText then
+                    local text = object:GetText()
+                    if text then
+                        local translated = BenillaUiText(text)
+                        if translated ~= text then object:SetText(translated) end
+                    end
+                end
+            end
+            caption(frame)
+            for _, region in ipairs({frame:GetRegions()}) do caption(region) end
+            for _, child in ipairs({frame:GetChildren()}) do BenillaUiLocalize(child) end
+        end
+
         -- One valueStep per step, where the reference's arrows and wheel move half the bar
         -- (UIPanelTemplates.xml:137/149, UIPanelTemplates.lua:150-157).
         -- Soundless: the reference plays UChatScrollButton on an arrow click, never on the wheel.
diff --git a/crates/benilla-app/src/glue_strings.rs b/crates/benilla-app/src/glue_strings.rs
index 5ef6d3d82..812534db3 100644
--- a/crates/benilla-app/src/glue_strings.rs
+++ b/crates/benilla-app/src/glue_strings.rs
@@ -149,6 +149,27 @@ pub(crate) fn table_from_chain(chain: &mut benilla_formats::Chain) -> GlueString
 mod tests {
     use super::*;
 
+    #[test]
+    fn the_russian_pack_localizes_glue_captions_as_utf8() {
+        let data = benilla_formats::wow_data_or_skip!();
+        let locale = benilla_formats::ClientLocale::RuRu;
+        if locale.pack_folder(&data).is_none() {
+            benilla_formats::skipped_optional("no ruRU language pack", &[data.join("ruRU")]);
+            return;
+        }
+        let mut chain = benilla_formats::Chain::open_localized(&data, locale).unwrap();
+        let table = table_from_chain(&mut chain);
+        for key in ["LOGIN", "ACCOUNT_NAME", "PASSWORD"] {
+            let caption = table.get(key).expect("localized glue caption");
+            assert!(
+                caption
+                    .chars()
+                    .any(|c| ('\u{0400}'..='\u{04ff}').contains(&c)),
+                "{key}: {caption}"
+            );
+        }
+    }
+
     #[test]
     fn parses_assignments_and_skips_the_rest() {
         let src = r#"
diff --git a/crates/benilla-app/src/lib.rs b/crates/benilla-app/src/lib.rs
index 1a0e200b2..85b3d839c 100644
--- a/crates/benilla-app/src/lib.rs
+++ b/crates/benilla-app/src/lib.rs
@@ -312,8 +312,19 @@ fn launch(build: BuildId, extend: Option<Extension<'_>>) -> AppExit {
     // absent and terrain loads fail gracefully.
     match benilla_formats::wow_data() {
         Some(data_dir) => {
+            let locale = match benilla_formats::ClientLocale::for_install(&data_dir) {
+                Ok(locale) => locale,
+                Err(e) => {
+                    eprintln!("benilla: {e:#}");
+                    return AppExit::error();
+                }
+            };
             if let Err(e) = benilla_assets::register_mpq_source(&mut app, &data_dir) {
                 eprintln!("benilla-assets: mpq:// source unavailable ({e:#})");
+                // A selected pack must not degrade into an English login with no client data.
+                if locale == benilla_formats::ClientLocale::RuRu {
+                    return AppExit::error();
+                }
             }
         }
         None => eprintln!(
diff --git a/crates/benilla-app/src/login/mod.rs b/crates/benilla-app/src/login/mod.rs
index 40308fea8..88e02b5ce 100644
--- a/crates/benilla-app/src/login/mod.rs
+++ b/crates/benilla-app/src/login/mod.rs
@@ -147,6 +147,7 @@ pub(super) struct Attempt<'w> {
     submit: Res<'w, LoginSubmit>,
     abandon: Res<'w, LoginAbandon>,
     realmlist: Res<'w, crate::realmlist::Realmlist>,
+    assets: Option<Res<'w, benilla_assets::WorldAssets>>,
 }
 
 impl Attempt<'_> {
@@ -161,6 +162,10 @@ impl Attempt<'_> {
             user: user.to_string(),
             pass: pass.to_string(),
             host: self.realmlist.address().to_string(),
+            locale: self.assets.as_ref().map_or(*b"enUS", |assets| {
+                use benilla_assets::LockRecover;
+                assets.chain.lock_recover().locale().auth_tag()
+            }),
             generation: self.abandon.0.load(Ordering::SeqCst),
         });
     }
diff --git a/crates/benilla-app/src/net/io.rs b/crates/benilla-app/src/net/io.rs
index c993d47c9..07236cf97 100644
--- a/crates/benilla-app/src/net/io.rs
+++ b/crates/benilla-app/src/net/io.rs
@@ -64,6 +64,8 @@ pub(crate) struct LoginRequest {
     /// The realmlist to dial, `host[:port]`, per attempt so an edit mid-dial cannot retarget the
     /// connection in flight.
     pub(crate) host: String,
+    /// The mounted client language captured at submit time, in canonical ASCII tag order.
+    pub(crate) locale: [u8; 4],
     pub(crate) generation: u64,
 }
 
@@ -355,7 +357,7 @@ fn run(
     // Logon: the dial and the SRP6 exchange against realmd.
     let mut logon = {
         stage(LoginStage::Connecting);
-        match benilla_protocol::logon(&req.host, &req.user, &req.pass) {
+        match benilla_protocol::logon_with_locale(&req.host, &req.user, &req.pass, req.locale) {
             Ok(l) => l,
             Err(e) => {
                 if canceled() {
diff --git a/crates/benilla-app/src/net/io/cycle_tests.rs b/crates/benilla-app/src/net/io/cycle_tests.rs
index c30a155f2..35e9f60a1 100644
--- a/crates/benilla-app/src/net/io/cycle_tests.rs
+++ b/crates/benilla-app/src/net/io/cycle_tests.rs
@@ -248,6 +248,7 @@ fn an_empty_account_parks_at_select_without_creating_a_character() {
             user: USER.into(),
             pass: PASS.into(),
             host: realmd,
+            locale: *b"enUS",
             generation: 0,
         })
         .unwrap();
diff --git a/crates/benilla-app/src/ui_script/escape_tests.rs b/crates/benilla-app/src/ui_script/escape_tests.rs
index d57cf4e16..73eed71b4 100644
--- a/crates/benilla-app/src/ui_script/escape_tests.rs
+++ b/crates/benilla-app/src/ui_script/escape_tests.rs
@@ -488,6 +488,7 @@ fn an_addon_frame_registered_in_uispecialframes_closes_on_escape() {
     load_xml(&s, r"Interface\FrameXML\UIPanelTemplates.xml");
     load_xml(&s, r"Interface\FrameXML\GameMenuFrame.xml");
     load_xml(&s, r"Interface\FrameXML\StaticPopup.xml");
+    load_xml(&s, "ScrollTemplates.xml");
     load_xml(&s, "GameMenuAdapters.xml");
 
     s.run(
diff --git a/crates/benilla-app/src/ui_script/game_menu_tests.rs b/crates/benilla-app/src/ui_script/game_menu_tests.rs
index e14b38871..b8815fe0c 100644
--- a/crates/benilla-app/src/ui_script/game_menu_tests.rs
+++ b/crates/benilla-app/src/ui_script/game_menu_tests.rs
@@ -26,6 +26,7 @@ fn harness_with(extra: &[&str]) -> UiScript {
         r"Interface\FrameXML\UIPanelTemplates.xml",
         r"Interface\FrameXML\GameMenuFrame.xml",
         "Interface\\FrameXML\\StaticPopup.xml",
+        "ScrollTemplates.xml",
         "GameMenuAdapters.xml",
     ];
     for file in super::test_ui::production_order(&[MENU, extra]) {
diff --git a/crates/benilla-app/src/ui_script/lifecycle.rs b/crates/benilla-app/src/ui_script/lifecycle.rs
index d91c92bb9..83176dfde 100644
--- a/crates/benilla-app/src/ui_script/lifecycle.rs
+++ b/crates/benilla-app/src/ui_script/lifecycle.rs
@@ -32,7 +32,10 @@ fn install_boot_vm(world: &mut World) {
 /// A fresh VM on the process clock with the addon asset probes wired, or `None` (the world's VM
 /// removed) when the VM cannot start.
 fn new_vm(world: &mut World) -> Option<UiScript> {
-    let mut script = match UiScript::new() {
+    let locale = world
+        .get_resource::<benilla_assets::WorldAssets>()
+        .map_or("enUS", |assets| assets.chain.lock_recover().locale().code());
+    let mut script = match UiScript::new_with_locale(locale) {
         Ok(s) => s,
         Err(e) => {
             error!("ui_script: VM init failed: {e}");
diff --git a/crates/benilla-app/src/ui_script/options_tests.rs b/crates/benilla-app/src/ui_script/options_tests.rs
index 4b4917f72..41513587b 100644
--- a/crates/benilla-app/src/ui_script/options_tests.rs
+++ b/crates/benilla-app/src/ui_script/options_tests.rs
@@ -8,6 +8,102 @@ fn harness() -> UiScript {
     harness_on(UiScript::new().unwrap())
 }
 
+#[test]
+fn the_russian_pack_localizes_the_window_search_and_dropdown_without_changing_values() {
+    let data = benilla_formats::wow_data_or_skip!();
+    if benilla_formats::ClientLocale::RuRu
+        .pack_folder(&data)
+        .is_none()
+    {
+        benilla_formats::skipped_optional("no ruRU language pack", &[data.join("ruRU")]);
+        return;
+    }
+    let mut s = UiScript::new_with_locale("ruRU").unwrap();
+    s.register_cvars(crate::cvars::registered_pairs());
+    s.set_cvar_host("gxWindow", "0");
+    let mut s = harness_on(s);
+    s.run("ShowUIPanel(BenillaOptionsFrame)").unwrap();
+    let labels: Vec<String> = s.eval(r#"
+        local labels = {}
+        for page, rows in pairs(BENILLA_OPTIONS_PAGE_ROWS) do
+            for _, row in ipairs(rows) do
+                local label = getglobal("BenillaOptionsFrameContainerBody" .. page .. row .. "Label")
+                if label then table.insert(labels, label:GetText() or "") end
+            end
+        end
+        return labels
+    "#).unwrap();
+    assert!(labels.len() > 70, "the settings rows were enumerated");
+    for label in labels {
+        assert!(
+            label
+                .chars()
+                .any(|c| ('\u{0400}'..='\u{04ff}').contains(&c)),
+            "unlocalized settings label: {label}"
+        );
+    }
+    assert!(s.eval::<bool>(
+        "return BenillaOptionsFrameContainerTitle:GetText() == CONTROLS_LABEL and CONTROLS_LABEL ~= 'Controls'"
+    ).unwrap());
+    assert_eq!(
+        s.eval::<String>("return GameMenuButtonOptions:GetText()")
+            .unwrap(),
+        "Настройки"
+    );
+    assert_eq!(
+        s.eval::<String>("return BenillaUiUpper('МуЗыКа ёж')")
+            .unwrap(),
+        "МУЗЫКА ЁЖ"
+    );
+    for query in ["музы", "МУЗЫ"] {
+        s.run(&format!("BenillaOptionsFrameSearchBox:SetText('{query}')"))
+            .unwrap();
+        s.tick(0.0);
+        assert_eq!(
+            s.eval::<String>("return BenillaOptionsFrameContainerTitle:GetText()")
+                .unwrap(),
+            "Результаты поиска"
+        );
+        assert!(s
+            .eval::<bool>("return BenillaOptionsFrameContainerBodyAudioRowMusic:IsVisible()")
+            .unwrap());
+        assert!(!s
+            .eval::<bool>("return BenillaOptionsFrameContainerBodyNoResults:IsVisible()")
+            .unwrap());
+    }
+    s.run("BenillaOptionsFrameCategoryListRowGraphics:Click()")
+        .unwrap();
+    // Clearing the search drains OnTextChanged on the next frame, restoring the hidden rows.
+    s.tick(0.0);
+    assert!(s.errors().is_empty(), "script errors: {:?}", s.errors());
+    const ROW: &str = "BenillaOptionsFrameContainerBodyGraphicsRowDisplayMode";
+    assert_eq!(
+        s.eval::<String>(&format!("return {ROW}Label:GetText()"))
+            .unwrap(),
+        "Режим экрана"
+    );
+    assert_eq!(
+        s.eval::<String>(&format!("return {ROW}DropdownText:GetText()"))
+            .unwrap(),
+        "Оконный (на весь экран)"
+    );
+    s.take_cvar_changes();
+    s.run(&format!(
+        "{ROW}DropdownButton:Click(); DropDownList1Button2:Click()"
+    ))
+    .unwrap();
+    assert_eq!(
+        s.eval::<String>(&format!("return {ROW}DropdownText:GetText()"))
+            .unwrap(),
+        "Оконный"
+    );
+    assert_eq!(
+        s.take_cvar_changes(),
+        vec![("gxWindow".to_string(), "1".to_string())]
+    );
+    assert!(s.errors().is_empty(), "script errors: {:?}", s.errors());
+}
+
 /// Load the manifest slice onto `s`, so a page test can seed CVars before the XML loads, as the
 /// app does. GameTooltip.xml precedes UIDropDownMenu.xml for the kit's `TOOLTIP_DEFAULT_COLOR`.
 fn harness_on(s: UiScript) -> UiScript {
diff --git a/crates/benilla-app/src/ui_script/reference_ui.rs b/crates/benilla-app/src/ui_script/reference_ui.rs
index 80ad2df53..cc84ca215 100644
--- a/crates/benilla-app/src/ui_script/reference_ui.rs
+++ b/crates/benilla-app/src/ui_script/reference_ui.rs
@@ -101,7 +101,12 @@ fn chain() -> Option<&'static Chain> {
                 );
                 return None;
             };
-            match benilla_formats::open_chain(&data) {
+            // Reference assertions use the base chain; the running client uses its language pack.
+            #[cfg(test)]
+            let opened = Chain::open(&data);
+            #[cfg(not(test))]
+            let opened = Chain::open_client(&data);
+            match opened {
                 Ok(chain) => Some(chain),
                 Err(e) => {
                     error!("ui_script: opening the patch chain to source the reference UI: {e:#}");
@@ -121,6 +126,7 @@ pub(super) mod fixture {
 
     thread_local! {
         static OVERLAY: RefCell<HashMap<String, Option<Vec<u8>>>> = RefCell::new(HashMap::new());
+        static SELECTED_CHAIN: RefCell<Option<benilla_formats::Chain>> = const { RefCell::new(None) };
     }
 
     fn key(path: &str) -> String {
@@ -141,7 +147,32 @@ pub(super) mod fixture {
 
     /// The overlay's answer for `path`, `None` when it has no entry.
     pub(super) fn read(path: &str) -> Option<Option<Vec<u8>>> {
-        OVERLAY.with(|o| o.borrow().get(&key(path)).cloned())
+        OVERLAY
+            .with(|o| o.borrow().get(&key(path)).cloned())
+            .or_else(|| {
+                SELECTED_CHAIN
+                    .with(|chain| chain.borrow().as_ref().map(|chain| chain.read(path).ok()))
+            })
+    }
+
+    /// Read an actual selected install chain through the production loader on this test thread.
+    pub(in crate::ui_script) fn use_chain(chain: benilla_formats::Chain) -> ChainGuard {
+        SELECTED_CHAIN.with(|selected| {
+            let mut selected = selected.borrow_mut();
+            assert!(selected.is_none(), "a chain fixture cannot nest");
+            *selected = Some(chain);
+        });
+        ChainGuard
+    }
+
+    pub(in crate::ui_script) struct ChainGuard;
+
+    impl Drop for ChainGuard {
+        fn drop(&mut self) {
+            SELECTED_CHAIN.with(|selected| {
+                selected.borrow_mut().take();
+            });
+        }
     }
 
     /// Clears the overlay on drop.
diff --git a/crates/benilla-app/src/ui_script/shipped_xml_tests.rs b/crates/benilla-app/src/ui_script/shipped_xml_tests.rs
index 800d1b74b..822a46205 100644
--- a/crates/benilla-app/src/ui_script/shipped_xml_tests.rs
+++ b/crates/benilla-app/src/ui_script/shipped_xml_tests.rs
@@ -45,6 +45,54 @@ fn the_whole_shipped_manifest_loads_without_errors() {
     assert!(s.errors().is_empty(), "script errors: {:?}", s.errors());
 }
 
+#[test]
+fn the_russian_pack_loads_the_complete_interface_and_takes_variables_loaded() {
+    let data = benilla_formats::wow_data_or_skip!();
+    let locale = benilla_formats::ClientLocale::RuRu;
+    if locale.pack_folder(&data).is_none() {
+        benilla_formats::skipped_optional("no ruRU language pack", &[data.join("ruRU")]);
+        return;
+    }
+    let chain = benilla_formats::Chain::open_localized(&data, locale).unwrap();
+    let _selected = super::reference_ui::fixture::use_chain(chain);
+    let mut s = benilla_ui::script::UiScript::new_with_locale(locale.code()).unwrap();
+    s.set_screen_size(1024.0, 768.0);
+    s.set_unit(
+        "player",
+        Some(benilla_ui::script::UnitState {
+            exists: true,
+            name: Some("Probefour".into()),
+            level: 60,
+            ..Default::default()
+        }),
+    );
+    let failures = super::load_default_ui(&s);
+    assert!(
+        failures.is_empty(),
+        "Russian manifest load errors: {failures:#?}"
+    );
+    assert!(s
+        .eval::<bool>("return GetLocale() == 'ruRU' and LOCALE_ruRU == true")
+        .unwrap());
+    let cancel = s.eval::<String>("return CANCEL").unwrap();
+    assert!(cancel
+        .chars()
+        .any(|c| ('\u{0400}'..='\u{04ff}').contains(&c)));
+    assert_eq!(
+        s.eval::<String>("return GameMenuButtonOptions:GetText()")
+            .unwrap(),
+        "Настройки"
+    );
+    s.fire_event("VARIABLES_LOADED", vec![]);
+    s.run("ShowUIPanel(BenillaOptionsFrame)").unwrap();
+    s.resolve();
+    assert!(
+        s.errors().is_empty(),
+        "Russian interface script errors: {:?}",
+        s.errors()
+    );
+}
+
 /// Loading the UI makes no sound: a dropdown's OnLoad runs `UIDropDownMenu_Initialize`, which calls
 /// its init at once (`UIDropDownMenu.lua:50`), and a unit popup's init reaches `UnitPopup_ShowMenu`
 /// and its closing `PlaySound("igMainMenuOpen")` unless `UnitPopup_HideButtons` leaves only CANCEL
diff --git a/crates/benilla-app/src/ui_script/test_ui.rs b/crates/benilla-app/src/ui_script/test_ui.rs
index 89be697eb..78fe443d1 100644
--- a/crates/benilla-app/src/ui_script/test_ui.rs
+++ b/crates/benilla-app/src/ui_script/test_ui.rs
@@ -88,6 +88,26 @@ fn load_entry(s: &UiScript, entry: &str, strict_templates: bool, no_warnings: bo
     // The app registers its CVars before any file loads: stock `UIOptionsFrame.xml` reads two
     // camera CVars at `OnLoad` and raises on a nil. A value a test already set stands.
     s.register_cvars(crate::cvars::registered_pairs());
+    // A localized VM reads the same selected patch chain as production; English kits keep the
+    // raw reference chain, independent of the process's WOW_LOCALE.
+    let chain = match s.eval::<String>("return GetLocale()").unwrap().as_str() {
+        "ruRU" => Some(
+            benilla_formats::Chain::open_localized(
+                &benilla_formats::wow_data().expect("a localized kit needs client data"),
+                benilla_formats::ClientLocale::RuRu,
+            )
+            .expect("the selected language pack"),
+        ),
+        _ => None,
+    };
+    let read = |req: &str| {
+        if let Some(chain) = &chain {
+            if super::reference_ui::is_chain_entry(req) {
+                return chain.read(req).ok();
+            }
+        }
+        read(req)
+    };
     let path = entry.replace('\\', "/");
     let bytes = read(&path).unwrap_or_else(|| panic!("{entry}: not found"));
     if path.to_ascii_lowercase().ends_with(".lua") {
diff --git a/crates/benilla-app/src/ui_text/engine/mod.rs b/crates/benilla-app/src/ui_text/engine/mod.rs
index b3bad4ccc..3ddf8ddcd 100644
--- a/crates/benilla-app/src/ui_text/engine/mod.rs
+++ b/crates/benilla-app/src/ui_text/engine/mod.rs
@@ -146,14 +146,14 @@ pub(crate) struct TextEngine {
 /// the database that can draw a character, so a system face would silently stand in for a client
 /// face. A character no client or addon face carries draws nothing, as in the reference, and
 /// measures 0. The locale only picks which language's family name a face answers to.
-fn client_font_system() -> FontSystem {
-    FontSystem::new_with_locale_and_db("en-US".to_string(), fontdb::Database::new())
+fn client_font_system(locale: benilla_formats::ClientLocale) -> FontSystem {
+    FontSystem::new_with_locale_and_db(locale.language_tag().to_string(), fontdb::Database::new())
 }
 
 impl TextEngine {
     /// Register the client TTFs off the patch chain; `None`, and no text, without Friz Quadrata.
     fn load(world_assets: &WorldAssets, images: &Assets<Image>, dpi: f32) -> Option<Self> {
-        let mut font_system = client_font_system();
+        let mut font_system = client_font_system(world_assets.chain.lock_recover().locale());
         let mut faces: Vec<Face> = Vec::new();
         let mut path_to_face = HashMap::new();
         for &path in CLIENT_FONTS {
@@ -603,7 +603,15 @@ fn read_font_bytes(source: &FontSource, path: &str) -> Option<Vec<u8>> {
 pub(super) fn test_engine(dpi: f32) -> Option<TextEngine> {
     let data = benilla_formats::wow_data()?;
     let chain = benilla_formats::open_chain(&data).ok()?;
-    let mut font_system = client_font_system();
+    test_engine_from_chain(chain, dpi)
+}
+
+#[cfg(test)]
+pub(super) fn test_engine_from_chain(
+    chain: benilla_formats::Chain,
+    dpi: f32,
+) -> Option<TextEngine> {
+    let mut font_system = client_font_system(chain.locale());
     let mut faces: Vec<Face> = Vec::new();
     let mut path_to_face = HashMap::new();
     for &path in CLIENT_FONTS {
@@ -810,6 +818,38 @@ mod differential_tests {
 mod ppem_tests {
     use super::*;
 
+    #[test]
+    fn the_russian_pack_rasterizes_cyrillic_in_every_client_face() {
+        let data = benilla_formats::wow_data_or_skip!();
+        let locale = benilla_formats::ClientLocale::RuRu;
+        if locale.pack_folder(&data).is_none() {
+            benilla_formats::skipped_optional("no ruRU language pack", &[data.join("ruRU")]);
+            return;
+        }
+        let chain = benilla_formats::Chain::open_localized(&data, locale).unwrap();
+        let mut e = test_engine_from_chain(chain, 1.0).expect("localized client fonts");
+        for &path in TEST_FACES {
+            let face = e.face_for(Some(path));
+            assert_eq!(e.faces[face].path, path);
+            e.ensure_str(face, 16, 0, "АаЯяЁё");
+            for ch in "АаЯяЁё".chars() {
+                let shaped = e
+                    .char_cell(face, 16, ch)
+                    .expect("a Cyrillic character shaped");
+                assert!(!shaped.glyphs.is_empty(), "{path}: {ch}");
+                for glyph in &shaped.glyphs {
+                    assert_ne!(glyph.glyph_id, 0, "{path}: {ch} must not be .notdef");
+                    let cell = e.cell(face, 16, 0, glyph.glyph_id).expect("Cyrillic ink");
+                    assert!(cell.px_w > 0.0 && cell.px_h > 0.0, "{path}: {ch}");
+                }
+            }
+        }
+        assert!(
+            e.substituted.is_empty(),
+            "Cyrillic uses the selected client faces"
+        );
+    }
+
     fn engine_or_skip() -> Option<TextEngine> {
         match test_engine(1.0) {
             Some(e) => Some(e),
diff --git a/crates/benilla-assets/src/lib.rs b/crates/benilla-assets/src/lib.rs
index c412f149a..d23cc7d2e 100644
--- a/crates/benilla-assets/src/lib.rs
+++ b/crates/benilla-assets/src/lib.rs
@@ -71,7 +71,7 @@ impl MpqAssetReader {
     /// Open the patch chain from a `Data` directory or a single `.MPQ`.
     pub fn open(data_dir: &Path) -> Result<Self> {
         Ok(Self {
-            chain: Arc::new(Chain::open(data_dir)?),
+            chain: Arc::new(Chain::open_client(data_dir)?),
         })
     }
 }
diff --git a/crates/benilla-formats/src/chain.rs b/crates/benilla-formats/src/chain.rs
index a84b26f34..40dc1619b 100644
--- a/crates/benilla-formats/src/chain.rs
+++ b/crates/benilla-formats/src/chain.rs
@@ -8,7 +8,7 @@ use std::path::Path;
 use anyhow::{anyhow, bail, Context, Result};
 use benilla_mpq::Archive;
 
-use crate::VANILLA_BASE_ORDER;
+use crate::{ClientLocale, VANILLA_BASE_ORDER};
 
 /// One entry from a chain listing: an internal path and its uncompressed size.
 pub struct ChainEntry {
@@ -20,6 +20,7 @@ pub struct ChainEntry {
 pub struct Chain {
     /// Ascending priority: later archives win.
     archives: Vec<Archive>,
+    locale: ClientLocale,
 }
 
 /// `patch-?.MPQ` as the reference's `FindFirstFileW` glob matches it (template `0x82edbc`, wrapper
@@ -93,7 +94,36 @@ impl Chain {
                 Archive::open(path).with_context(|| format!("opening MPQ {}", path.display()))?,
             );
         }
-        Ok(Self { archives })
+        Ok(Self {
+            archives,
+            locale: ClientLocale::EnUs,
+        })
+    }
+
+    /// Open the runtime chain with `$WOW_LOCALE`, or the installed ruRU pack when unset.
+    /// [`Self::open`] stays the unlocalized reference chain for extraction and reference tests.
+    pub fn open_client(path: &Path) -> Result<Self> {
+        Self::open_localized(path, ClientLocale::for_install(path)?)
+    }
+
+    /// Mount the selected language's archives after the vanilla chain. Missing files fall through
+    /// to the base archives; an explicitly selected missing or corrupt pack is an error.
+    pub fn open_localized(path: &Path, locale: ClientLocale) -> Result<Self> {
+        let mut chain = Self::open(path)?;
+        if locale == ClientLocale::RuRu && path.is_dir() {
+            let folder = crate::locale::locale_folder(path, locale)
+                .ok_or_else(|| anyhow!("ruRU language pack not found in {}", path.display()))?;
+            let overlay = Self::open(&folder)
+                .with_context(|| format!("opening {} language pack", locale.code()))?;
+            chain.archives.extend(overlay.archives);
+        }
+        chain.locale = locale;
+        Ok(chain)
+    }
+
+    /// The language mounted for this chain, also used by Lua and authentication.
+    pub fn locale(&self) -> ClientLocale {
+        self.locale
     }
 
     /// The highest-priority archive with an entry for `name`, a delete marker included, as a
@@ -178,6 +208,137 @@ impl Chain {
 mod tests {
     use super::*;
 
+    struct TestInstall(std::path::PathBuf);
+
+    impl TestInstall {
+        fn new() -> Self {
+            static NEXT: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(0);
+            let id = NEXT.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
+            let root =
+                std::env::temp_dir().join(format!("benilla-locale-{}-{id}", std::process::id()));
+            std::fs::create_dir(&root).unwrap();
+            std::fs::create_dir(root.join("RUrU")).unwrap();
+            // Valid empty V1 archives: the tables point at EOF and have zero entries.
+            let mut header = b"MPQ\x1a".to_vec();
+            for field in [32u32, 32, 3 << 16, 32, 32, 0, 0] {
+                header.extend_from_slice(&field.to_le_bytes());
+            }
+            for name in [
+                "dbc.MPQ",
+                "patch-2.MPQ",
+                "RUrU/patch-1.MPQ",
+                "RUrU/patch-3.MPQ",
+            ] {
+                std::fs::write(root.join(name), &header).unwrap();
+            }
+            Self(root)
+        }
+    }
+
+    impl Drop for TestInstall {
+        fn drop(&mut self) {
+            for name in [
+                "dbc.MPQ",
+                "patch-2.MPQ",
+                "RUrU/patch-1.MPQ",
+                "RUrU/patch-3.MPQ",
+            ] {
+                let _ = std::fs::remove_file(self.0.join(name));
+            }
+            let _ = std::fs::remove_dir(self.0.join("RUrU"));
+            let _ = std::fs::remove_dir(&self.0);
+        }
+    }
+
+    #[test]
+    fn language_archives_mount_after_base_patches_and_english_is_isolated() {
+        let install = TestInstall::new();
+        assert_eq!(
+            ClientLocale::select(&install.0, None).unwrap(),
+            ClientLocale::RuRu
+        );
+        assert_eq!(
+            ClientLocale::select(&install.0, Some("enUS")).unwrap(),
+            ClientLocale::EnUs
+        );
+        let russian = Chain::open_localized(&install.0, ClientLocale::RuRu).unwrap();
+        let mounted: Vec<_> = russian
+            .archives
+            .iter()
+            .map(|a| {
+                a.path()
+                    .strip_prefix(&install.0)
+                    .unwrap()
+                    .to_string_lossy()
+                    .replace('\\', "/")
+            })
+            .collect();
+        assert_eq!(
+            mounted,
+            [
+                "dbc.MPQ",
+                "patch-2.MPQ",
+                "RUrU/patch-1.MPQ",
+                "RUrU/patch-3.MPQ"
+            ]
+        );
+        assert_eq!(russian.locale(), ClientLocale::RuRu);
+        let english = Chain::open_localized(&install.0, ClientLocale::EnUs).unwrap();
+        assert_eq!(english.archives.len(), 2);
+        assert_eq!(english.locale(), ClientLocale::EnUs);
+    }
+
+    #[test]
+    fn a_missing_or_corrupt_selected_language_is_not_silently_english() {
+        let install = TestInstall::new();
+        std::fs::write(install.0.join("RUrU/patch-1.MPQ"), b"corrupt").unwrap();
+        assert!(Chain::open_localized(&install.0, ClientLocale::RuRu).is_err());
+        assert!(Chain::open_localized(&install.0, ClientLocale::EnUs).is_ok());
+        for name in ["RUrU/patch-1.MPQ", "RUrU/patch-3.MPQ"] {
+            std::fs::remove_file(install.0.join(name)).unwrap();
+        }
+        std::fs::remove_dir(install.0.join("RUrU")).unwrap();
+        assert!(Chain::open_localized(&install.0, ClientLocale::RuRu).is_err());
+        assert_eq!(
+            ClientLocale::select(&install.0, None).unwrap(),
+            ClientLocale::EnUs
+        );
+    }
+
+    #[test]
+    fn the_installed_russian_pack_localizes_spell_names_and_keeps_base_fallbacks() {
+        let data = crate::wow_data_or_skip!();
+        if crate::locale::locale_folder(&data, ClientLocale::RuRu).is_none() {
+            crate::skipped_optional("no ruRU language pack", &[data.join("ruRU")]);
+            return;
+        }
+        let mut russian = Chain::open_localized(&data, ClientLocale::RuRu).unwrap();
+        let mut english = Chain::open(&data).unwrap();
+        let names = crate::load_spell_catalog(&mut russian).expect("localized Spell.dbc layout");
+        let base_names = crate::load_spell_catalog(&mut english).unwrap();
+        let localized = &names.get(133).expect("Fireball").name;
+        assert!(localized
+            .chars()
+            .any(|c| ('\u{0400}'..='\u{04ff}').contains(&c)));
+        assert_ne!(localized, &base_names.get(133).unwrap().name);
+        let icons = "DBFilesClient\\SpellIcon.dbc";
+        assert_eq!(russian.read(icons).unwrap(), english.read(icons).unwrap());
+        for file in [
+            "Fonts\\FRIZQT__.TTF",
+            "Interface\\FrameXML\\GlobalStrings.lua",
+        ] {
+            let archive = russian.find_file_archive(file).expect("localized resource");
+            assert!(archive
+                .parent()
+                .unwrap()
+                .file_name()
+                .unwrap()
+                .to_string_lossy()
+                .eq_ignore_ascii_case("ruRU"));
+            assert_ne!(russian.read(file).unwrap(), english.read(file).unwrap());
+        }
+    }
+
     fn owned(names: &[&str]) -> Vec<String> {
         names.iter().map(|n| n.to_string()).collect()
     }
diff --git a/crates/benilla-formats/src/install.rs b/crates/benilla-formats/src/install.rs
index cab28469e..c0d1b8928 100644
--- a/crates/benilla-formats/src/install.rs
+++ b/crates/benilla-formats/src/install.rs
@@ -128,6 +128,18 @@ pub fn skipped(what: &str, looked_in: &[PathBuf]) {
         what,
         looked_in,
     );
+    log_skip(what);
+}
+
+/// A test requiring optional data (such as a language pack) records a skip even when the base
+/// install is required. A pack that exists but fails to open must still fail its test.
+#[doc(hidden)]
+pub fn skipped_optional(what: &str, looked_in: &[PathBuf]) {
+    skipped_under(false, what, looked_in);
+    log_skip(what);
+}
+
+fn log_skip(what: &str) {
     // `$BENILLA_SKIP_LOG`: libtest hides the line above, so the gate counts skips from this file.
     if let Some(log) = std::env::var_os("BENILLA_SKIP_LOG").filter(|p| !p.is_empty()) {
         use std::io::Write;
diff --git a/crates/benilla-formats/src/lib.rs b/crates/benilla-formats/src/lib.rs
index b6b4c932b..08f8e71c2 100644
--- a/crates/benilla-formats/src/lib.rs
+++ b/crates/benilla-formats/src/lib.rs
@@ -13,6 +13,8 @@ pub use benilla_blp::BlpTexels;
 
 mod chain;
 pub use chain::{Chain, ChainEntry};
+mod locale;
+pub use locale::ClientLocale;
 /// Loose `.tga` art, as addon folders ship it.
 mod tga;
 pub use tga::tga_to_rgba;
@@ -20,7 +22,7 @@ pub use tga::tga_to_rgba;
 mod install;
 pub use install::{
     addon_corpus, addon_corpus_candidates, candidates, project_folder, set_project_folder, skipped,
-    wow_data,
+    skipped_optional, wow_data,
 };
 mod characters;
 pub use characters::{
diff --git a/crates/benilla-formats/src/locale.rs b/crates/benilla-formats/src/locale.rs
new file mode 100644
index 000000000..a6da4ee97
--- /dev/null
+++ b/crates/benilla-formats/src/locale.rs
@@ -0,0 +1,124 @@
+//! The language of the client data, Lua UI and realmd challenge.
+//!
+//! Deviation: the community 1.12 ruRU pack lives in `Data/ruRU` and overlays the vanilla chain.
+//! Its DBCs keep the 1.12 layout and put Russian strings in slot zero, like the base tables.
+
+use std::path::{Path, PathBuf};
+
+use anyhow::{bail, Context, Result};
+
+/// The supported language packs. English reads the original vanilla chain unchanged.
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
+pub enum ClientLocale {
+    #[default]
+    EnUs,
+    RuRu,
+}
+
+impl ClientLocale {
+    /// The spelling returned by `GetLocale` and sent to realmd.
+    pub const fn code(self) -> &'static str {
+        match self {
+            Self::EnUs => "enUS",
+            Self::RuRu => "ruRU",
+        }
+    }
+
+    /// The four-character auth tag, before the protocol reverses its byte order.
+    pub const fn auth_tag(self) -> [u8; 4] {
+        match self {
+            Self::EnUs => *b"enUS",
+            Self::RuRu => *b"ruRU",
+        }
+    }
+
+    /// The optional language-pack folder under `Data`, found case-insensitively.
+    pub fn pack_folder(self, data: &Path) -> Option<PathBuf> {
+        locale_folder(data, self)
+    }
+
+    /// The language tag used for localized font family names.
+    pub const fn language_tag(self) -> &'static str {
+        match self {
+            Self::EnUs => "en-US",
+            Self::RuRu => "ru-RU",
+        }
+    }
+
+    /// Parse an explicit language; unknown values fail rather than silently loading another one.
+    pub fn from_code(code: &str) -> Result<Self> {
+        if code.eq_ignore_ascii_case("enUS") {
+            Ok(Self::EnUs)
+        } else if code.eq_ignore_ascii_case("ruRU") {
+            Ok(Self::RuRu)
+        } else {
+            bail!("unsupported client locale {code:?}; expected enUS, ruRU or auto");
+        }
+    }
+
+    /// Runtime selection: `$WOW_LOCALE=enUS|ruRU|auto`; unset or `auto` uses an installed ruRU
+    /// folder, otherwise English. Selection is made before any client resources load.
+    pub fn for_install(data: &Path) -> Result<Self> {
+        let selected = std::env::var("WOW_LOCALE").context("reading WOW_LOCALE");
+        match selected {
+            Ok(value) => Self::select(data, Some(&value)),
+            Err(_) if std::env::var_os("WOW_LOCALE").is_none() => Self::select(data, None),
+            Err(error) => Err(error),
+        }
+    }
+
+    pub(crate) fn select(data: &Path, value: Option<&str>) -> Result<Self> {
+        match value {
+            Some(code) if !code.eq_ignore_ascii_case("auto") => Self::from_code(code),
+            _ => Ok(if locale_folder(data, Self::RuRu).is_some() {
+                Self::RuRu
+            } else {
+                Self::EnUs
+            }),
+        }
+    }
+}
+
+/// Find the locale directory case-insensitively, including on a case-sensitive filesystem.
+pub(crate) fn locale_folder(data: &Path, locale: ClientLocale) -> Option<PathBuf> {
+    let mut folders: Vec<_> = std::fs::read_dir(data)
+        .ok()?
+        .filter_map(Result::ok)
+        .filter(|entry| {
+            entry.path().is_dir()
+                && entry
+                    .file_name()
+                    .to_string_lossy()
+                    .eq_ignore_ascii_case(locale.code())
+        })
+        .map(|entry| entry.path())
+        .collect();
+    folders.sort();
+    folders.into_iter().next()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn selection_is_explicit_and_unknown_values_are_errors() {
+        let absent = Path::new("/no-client-data-here");
+        assert_eq!(
+            ClientLocale::select(absent, None).unwrap(),
+            ClientLocale::EnUs
+        );
+        assert_eq!(
+            ClientLocale::select(absent, Some("auto")).unwrap(),
+            ClientLocale::EnUs
+        );
+        assert_eq!(
+            ClientLocale::select(absent, Some("RURU")).unwrap(),
+            ClientLocale::RuRu
+        );
+        for invalid in ["", "frFR", "../ruRU"] {
+            assert!(ClientLocale::select(absent, Some(invalid)).is_err());
+        }
+        assert_eq!(ClientLocale::RuRu.auth_tag(), *b"ruRU");
+    }
+}
diff --git a/crates/benilla-protocol/src/auth.rs b/crates/benilla-protocol/src/auth.rs
index 552ad5441..0c8ef9e78 100644
--- a/crates/benilla-protocol/src/auth.rs
+++ b/crates/benilla-protocol/src/auth.rs
@@ -69,6 +69,17 @@ pub fn write_logon_challenge(
     w: &mut impl Write,
     account_name: &str,
     build: u16,
+) -> std::io::Result<()> {
+    write_logon_challenge_with_locale(w, account_name, build, LOCALE_EN_US.to_be_bytes())
+}
+
+/// The challenge with the mounted client's locale, a four-character tag such as `ruRU`.
+/// realmd reverses the country bytes before matching the locale (`AuthSocket::ReadChallengeRequest`).
+pub fn write_logon_challenge_with_locale(
+    w: &mut impl Write,
+    account_name: &str,
+    build: u16,
+    locale: [u8; 4],
 ) -> std::io::Result<()> {
     // Everything after the 2-byte size field, assembled first so we can prefix its length.
     let mut body = Vec::with_capacity(34 + account_name.len());
@@ -79,7 +90,7 @@ pub fn write_logon_challenge(
     body.extend_from_slice(&build.to_le_bytes());
     body.extend_from_slice(&PLATFORM_X86.to_le_bytes());
     body.extend_from_slice(&client_os().to_le_bytes());
-    body.extend_from_slice(&LOCALE_EN_US.to_le_bytes());
+    body.extend_from_slice(&u32::from_be_bytes(locale).to_le_bytes());
     body.extend_from_slice(&0u32.to_le_bytes()); // utc_timezone_offset
     body.extend_from_slice(&Ipv4Addr::LOCALHOST.octets()); // client_ip_address (network order)
     body.push(account_name.len() as u8);
@@ -289,6 +300,20 @@ pub fn read_realm_list(r: &mut impl Read) -> Result<Vec<RealmInfo>> {
 mod tests {
     use super::*;
 
+    #[test]
+    fn the_logon_challenge_carries_the_selected_locale_in_wire_order() {
+        let mut english = Vec::new();
+        write_logon_challenge(&mut english, "PROBE", 5875).unwrap();
+        let mut explicit = Vec::new();
+        write_logon_challenge_with_locale(&mut explicit, "PROBE", 5875, *b"enUS").unwrap();
+        assert_eq!(explicit, english);
+        let mut russian = Vec::new();
+        write_logon_challenge_with_locale(&mut russian, "PROBE", 5875, *b"ruRU").unwrap();
+        assert_eq!(&russian[21..25], b"URur");
+        assert_eq!(&russian[..21], &english[..21]);
+        assert_eq!(&russian[25..], &english[25..]);
+    }
+
     #[test]
     fn os_tags_reverse_to_the_names_servers_match_on() {
         let spelled = |tag: u32| {
diff --git a/crates/benilla-protocol/src/lib.rs b/crates/benilla-protocol/src/lib.rs
index 23deefb58..d6b6a0108 100644
--- a/crates/benilla-protocol/src/lib.rs
+++ b/crates/benilla-protocol/src/lib.rs
@@ -165,6 +165,17 @@ impl Logon {
 
 /// The full SRP6 logon against a vanilla `realmd`, then the realm list.
 pub fn logon(host: &str, username: &str, password: &str) -> Result<Logon> {
+    logon_with_locale(host, username, password, *b"enUS")
+}
+
+/// The SRP6 logon with the client's selected four-character locale tag, used by the server for
+/// localized world responses. [`logon`] retains the English default for protocol instruments.
+pub fn logon_with_locale(
+    host: &str,
+    username: &str,
+    password: &str,
+    locale: [u8; 4],
+) -> Result<Logon> {
     let (host, port) = host_port(host, AUTH_PORT);
 
     let username_n =
@@ -179,8 +190,13 @@ pub fn logon(host: &str, username: &str, password: &str) -> Result<Logon> {
         let mut dialed = None;
         for _ in 0..MAX_CHALLENGE_DIALS {
             let mut stream = dial(host, port)?;
-            auth::write_logon_challenge(&mut stream, &username.to_uppercase(), CLIENT_BUILD)
-                .context("sending logon challenge")?;
+            auth::write_logon_challenge_with_locale(
+                &mut stream,
+                &username.to_uppercase(),
+                CLIENT_BUILD,
+                locale,
+            )
+            .context("sending logon challenge")?;
             let reply =
                 auth::read_challenge_reply(&mut stream).context("reading logon challenge reply")?;
             let server_public_key = PublicKey::from_le_bytes(reply.server_public_key)
diff --git a/crates/benilla-ui/src/script/client.rs b/crates/benilla-ui/src/script/client.rs
index c242e4d05..322d4fd1d 100644
--- a/crates/benilla-ui/src/script/client.rs
+++ b/crates/benilla-ui/src/script/client.rs
@@ -11,16 +11,16 @@ const VERSION: &str = "1.12.1";
 const BUILD: &str = "5875";
 const BUILD_DATE: &str = "Sep 19 2006";
 
-pub(super) fn install(lua: &Lua) -> mlua::Result<()> {
+pub(super) fn install(lua: &Lua, locale: &str) -> mlua::Result<()> {
     let g = lua.globals();
 
-    // `GetLocale()` (glue `0x46ce40`, in-game `0x48d8b0`) returns one string, `enUS`, as benilla
-    // is enUS-only. `IsMacClient()` (`0x48c980`) returns one nil, the PC build's answer, which
-    // takes FrameXML's PC key-label arm.
+    // `GetLocale()` (glue `0x46ce40`, in-game `0x48d8b0`) returns the mounted client language.
+    let locale = locale.to_string();
     g.set(
         "GetLocale",
-        lua.create_function(|lua, ()| lua.create_string("enUS"))?,
+        lua.create_function(move |lua, ()| lua.create_string(&locale))?,
     )?;
+    // `IsMacClient()` (`0x48c980`) is the PC build's nil answer, used for key labels.
     g.set("IsMacClient", lua.create_function(|_, ()| Ok(Value::Nil))?)?;
     // The PC build's other two platform answers: `IsWindowsClient()` (`0x48c960`) pushes the
     // number 1 and `IsLinuxClient()` (`0x48c990`) one nil. Arguments are ignored.
@@ -312,6 +312,28 @@ mod tests {
         );
     }
 
+    #[test]
+    fn locale_is_available_before_addons_run_and_is_specific_to_each_vm() {
+        let russian = UiScript::new_with_locale("ruRU").unwrap();
+        russian
+            .run("if GetLocale() == 'ruRU' then LocaleProbe = 'Русский' end")
+            .unwrap();
+        assert_eq!(
+            russian.eval::<String>("return LocaleProbe").unwrap(),
+            "Русский"
+        );
+        assert_eq!(russian.arity("GetLocale()").unwrap(), 1);
+        let english = UiScript::new().unwrap();
+        assert_eq!(
+            english.eval::<String>("return GetLocale()").unwrap(),
+            "enUS"
+        );
+        assert_eq!(
+            russian.eval::<String>("return GetLocale()").unwrap(),
+            "ruRU"
+        );
+    }
+
     /// The reference's arities: `GetLocale` (`0x48d8b0`) one string, `IsMacClient` (`0x48c980`)
     /// one nil.
     #[test]
diff --git a/crates/benilla-ui/src/script/mod.rs b/crates/benilla-ui/src/script/mod.rs
index 39128a767..03af78ae0 100644
--- a/crates/benilla-ui/src/script/mod.rs
+++ b/crates/benilla-ui/src/script/mod.rs
@@ -489,6 +489,11 @@ pub fn addon_chunk_name(folder: &str, file: &str) -> String {
 impl UiScript {
     /// Build a fully sandboxed, stdlib- and object-model-equipped host.
     pub fn new() -> mlua::Result<UiScript> {
+        Self::new_with_locale("enUS")
+    }
+
+    /// Build the host for the mounted client language, before FrameXML or addons run.
+    pub fn new_with_locale(locale: &str) -> mlua::Result<UiScript> {
         let lua = Lua::new();
         lua.set_app_data(Model::new());
         // Before anything can fire a handler and while no app-data borrow is held, as the
@@ -502,7 +507,7 @@ impl UiScript {
         chat_misc::install(&lua)?;
         channel::install(&lua)?;
         chat_window::install(&lua)?;
-        client::install(&lua)?;
+        client::install(&lua, locale)?;
         screenshot::install(&lua)?;
         stdlib::sandbox(&lua)?;
         // Before the stdlib layer, so its aliases bind the 5.0-shaped functions.
diff --git a/crates/benilla-ui/src/script/stdlib.rs b/crates/benilla-ui/src/script/stdlib.rs
index f62414078..b45f2677e 100644
--- a/crates/benilla-ui/src/script/stdlib.rs
+++ b/crates/benilla-ui/src/script/stdlib.rs
@@ -239,8 +239,6 @@ end
 function getglobal(name) return _G[name] end
 function setglobal(name, value) _G[name] = value end
 
--- ── GetLocale: benilla ships/reads enUS data only (the 5875 MPQs + Spell.dbc enUS column) ──────
-function GetLocale() return "enUS" end
 
 -- ── NOT here: wipe / tostringall / strsplit / strjoin / strconcat / strtrim ────────────────────
 -- Six 2.0+ names benilla used to define. 1.12 has none of them (absent from
diff --git a/crates/benilla-ui/src/script/tests/frame_api.rs b/crates/benilla-ui/src/script/tests/frame_api.rs
index fc9c20c53..e6d43c7c4 100644
--- a/crates/benilla-ui/src/script/tests/frame_api.rs
+++ b/crates/benilla-ui/src/script/tests/frame_api.rs
@@ -6,7 +6,7 @@ use super::common::script;
 fn get_locale_and_set_all_points() {
     let mut s = script();
     s.set_screen_size(800.0, 600.0);
-    // `GetLocale`: benilla is enUS-only.
+    // A VM with no selected language retains the English default.
     assert_eq!(s.eval::<String>("return GetLocale()").unwrap(), "enUS");
 
     s.run(
diff --git a/crates/benilla-world/src/assets/mod.rs b/crates/benilla-world/src/assets/mod.rs
index 0af2c64ec..a33e8169b 100644
--- a/crates/benilla-world/src/assets/mod.rs
+++ b/crates/benilla-world/src/assets/mod.rs
@@ -6,7 +6,7 @@ use bevy::render::renderer::RenderDevice;
 
 use crate::art_scope::{ArtScope, ArtSlot};
 use benilla_assets::{AssetSet, RenderConfig, WorldAssets};
-use benilla_formats::open_chain;
+use benilla_formats::Chain;
 
 /// Opens the patch chain at startup and inserts the shared [`WorldAssets`] and [`RenderConfig`].
 pub(crate) struct AssetPlugin;
@@ -65,8 +65,11 @@ fn open_world_assets(mut commands: Commands, device: Res<RenderDevice>) {
         .unwrap_or(1);
     commands.insert_resource(RenderConfig { unload_budget });
 
-    match open_chain(&data) {
-        Ok(chain) => commands.insert_resource(WorldAssets::open(chain, light_buf)),
+    match Chain::open_client(&data) {
+        Ok(chain) => {
+            info!("client data: locale {}", chain.locale().code());
+            commands.insert_resource(WorldAssets::open(chain, light_buf));
+        }
         Err(e) => error!("failed to open client data: {e:#}"),
     }
 }
diff --git a/crates/moonwell-deploy/src/package.rs b/crates/moonwell-deploy/src/package.rs
index fe8c2bf2f..7483cf22c 100644
--- a/crates/moonwell-deploy/src/package.rs
+++ b/crates/moonwell-deploy/src/package.rs
@@ -53,8 +53,8 @@ fn valid_auth_host(host: &str) -> bool {
         })
 }
 
-fn validate_data(data: &Path) -> Result<Vec<std::path::PathBuf>> {
-    ensure!(data.is_dir(), "vanilla Data directory was not found");
+fn mounted_archives(data: &Path) -> Result<Vec<std::path::PathBuf>> {
+    ensure!(data.is_dir(), "Data directory was not found");
     let mut names = HashSet::new();
     let mut files = Vec::new();
     for entry in fs::read_dir(data)? {
@@ -82,13 +82,27 @@ fn validate_data(data: &Path) -> Result<Vec<std::path::PathBuf>> {
         );
         files.push(entry.path());
     }
+    files.sort();
+    Ok(files)
+}
+
+fn validate_data(data: &Path) -> Result<Vec<std::path::PathBuf>> {
+    let files = mounted_archives(data)?;
+    let names: HashSet<_> = files
+        .iter()
+        .map(|p| {
+            p.file_name()
+                .unwrap()
+                .to_string_lossy()
+                .to_ascii_lowercase()
+        })
+        .collect();
     for base in BASE_ARCHIVES {
         ensure!(
             names.contains(*base),
             "missing vanilla base archive: {base}"
         );
     }
-    files.sort();
     // Modified installs can mimic vanilla archive names; check the winning 5875 Spell.dbc too.
     let mut spell_archives: Vec<_> = files.iter().collect();
     // Match benilla-formats' vanilla mount order, including speech2's final priority.
@@ -133,6 +147,44 @@ fn validate_data(data: &Path) -> Result<Vec<std::path::PathBuf>> {
     Ok(files)
 }
 
+/// Only mounted archives from the optional 1.12 Russian overlay; unrelated locale files stay out.
+fn russian_archives(data: &Path) -> Result<Vec<std::path::PathBuf>> {
+    let mut folders = Vec::new();
+    for entry in fs::read_dir(data)? {
+        let entry = entry?;
+        if entry
+            .file_name()
+            .to_string_lossy()
+            .eq_ignore_ascii_case("ruRU")
+            && entry.path().is_dir()
+        {
+            folders.push(entry.path());
+        }
+    }
+    ensure!(folders.len() <= 1, "duplicate ruRU language folders");
+    let Some(folder) = folders.first() else {
+        return Ok(Vec::new());
+    };
+    let archives = mounted_archives(folder)?;
+    ensure!(
+        !archives.is_empty(),
+        "ruRU language pack has no mounted archives"
+    );
+    for archive in &archives {
+        let archive = benilla_mpq::Archive::open(archive)?;
+        if archive.contains(r"DBFilesClient\Spell.dbc") {
+            let bytes = archive.read_file(r"DBFilesClient\Spell.dbc")?;
+            ensure!(
+                bytes.len() >= 20
+                    && &bytes[..4] == b"WDBC"
+                    && u32::from_le_bytes(bytes[8..12].try_into().unwrap()) == 173,
+                "ruRU Spell.dbc is not the vanilla 5875 layout"
+            );
+        }
+    }
+    Ok(archives)
+}
+
 fn ensure_outside(input: &Path, output: &Path) -> Result<()> {
     let input = input.canonicalize()?;
     let absolute = if output.is_absolute() {
@@ -143,12 +195,26 @@ fn ensure_outside(input: &Path, output: &Path) -> Result<()> {
     let parent = absolute
         .parent()
         .context("output needs a parent directory")?;
-    fs::create_dir_all(parent)?;
     let output = if absolute.exists() {
         absolute.canonicalize()?
     } else {
-        parent
+        // Resolve through the nearest existing ancestor without creating anything in an input.
+        let mut existing = parent;
+        while !existing.exists() {
+            existing = existing
+                .parent()
+                .context("output has no existing ancestor")?;
+        }
+        let suffix = parent.strip_prefix(existing)?;
+        ensure!(
+            !suffix
+                .components()
+                .any(|c| matches!(c, std::path::Component::ParentDir)),
+            "a nonexistent output parent cannot contain .."
+        );
+        existing
             .canonicalize()?
+            .join(suffix)
             .join(absolute.file_name().context("output needs a filename")?)
     };
     ensure!(
@@ -174,8 +240,10 @@ pub fn pack(source: &Path, output: &Path) -> Result<()> {
             .file_name()
             .into_string()
             .map_err(|_| anyhow::anyhow!("non-UTF-8 patch name"))?;
-        ensure!(patch.file_type()?.is_dir() && patch_name(&name),
-            "unsupported vanilla patch source: {name}; locale subdirectories are not supported by the client");
+        ensure!(
+            patch.file_type()?.is_dir() && patch_name(&name),
+            "unsupported vanilla patch source: {name}; expected a Data/patch-? source directory"
+        );
         let target = output.join("Data").join(format!("{name}.MPQ"));
         ensure!(
             !target.exists(),
@@ -274,6 +342,7 @@ pub fn validate_distribution(root: &Path) -> Result<()> {
         "MoonWell binary is not a native executable"
     );
     validate_data(&root.join("Data"))?;
+    russian_archives(&root.join("Data"))?;
     ensure!(
         root.join("realmlist.wtf").is_file(),
         "realmlist.wtf is missing"
@@ -294,7 +363,12 @@ pub fn stage(
         "auth host must be hostname or IPv4[:port]"
     );
     let archives = validate_data(data)?;
+    let localized = russian_archives(data)?;
     ensure_outside(data, output)?;
+    if let Some(archive) = localized.first() {
+        // A locale directory may point outside Data; it remains a read-only input as well.
+        ensure_outside(archive.parent().context("language pack directory")?, output)?;
+    }
     ensure_outside(binary, output)?;
     if let Some(source) = source {
         ensure_outside(source, output)?;
@@ -311,7 +385,7 @@ pub fn stage(
         ),
         "use a MoonWell player executable or .app"
     );
-    fs::create_dir(output)?;
+    fs::create_dir_all(output)?;
     if binary.is_dir() {
         for entry in WalkDir::new(binary).follow_links(false) {
             let entry = entry?;
@@ -350,6 +424,16 @@ pub fn stage(
             fs::copy(&archive, dest)?;
         }
     }
+    if !localized.is_empty() {
+        let locale_data = target_data.join("ruRU");
+        fs::create_dir(&locale_data)?;
+        for archive in localized {
+            fs::copy(
+                &archive,
+                locale_data.join(archive.file_name().expect("archive name")),
+            )?;
+        }
+    }
     fs::write(
         output.join("realmlist.wtf"),
         format!("set realmlist {host}\n"),
@@ -414,6 +498,10 @@ mod tests {
             crate::vanilla_mpq::normalize(&data.join(name)).unwrap();
         }
         let original = fs::read(data.join("patch-m.mpq")).unwrap();
+        let locale = data.join("RURU");
+        fs::create_dir(&locale).unwrap();
+        fs::copy(data.join("dbc.mpq"), locale.join("patch-1.MPQ")).unwrap();
+        fs::write(locale.join("notes.txt"), b"not a mounted archive").unwrap();
         let source = temp.path().join("src");
         fs::create_dir_all(source.join("Data/patch-M")).unwrap();
         fs::write(source.join("Data/patch-M/Test.txt"), b"custom").unwrap();
@@ -422,6 +510,11 @@ mod tests {
         let out = temp.path().join("out");
         stage(&binary, &data, &out, Some(&source), "127.0.0.1:3724").unwrap();
         assert_eq!(fs::read(data.join("patch-m.mpq")).unwrap(), original);
+        assert_eq!(
+            fs::read(out.join("Data/ruRU/patch-1.MPQ")).unwrap(),
+            fs::read(locale.join("patch-1.MPQ")).unwrap()
+        );
+        assert!(!out.join("Data/ruRU/notes.txt").exists());
         let archive = benilla_mpq::Archive::open(out.join("Data/patch-M.MPQ")).unwrap();
         assert_eq!(archive.read_file("Test.txt").unwrap(), b"custom");
         assert_eq!(
@@ -450,4 +543,40 @@ mod tests {
             .unwrap();
         assert!(validate_data(temp.path()).is_err());
     }
+
+    #[test]
+    fn a_wrath_spell_table_in_a_russian_overlay_is_rejected() {
+        let temp = tempfile::tempdir().unwrap();
+        let locale = temp.path().join("ruRU");
+        fs::create_dir(&locale).unwrap();
+        let mut spell = [0u8; 20];
+        spell[..4].copy_from_slice(b"WDBC");
+        spell[8..12].copy_from_slice(&234u32.to_le_bytes());
+        let archive = locale.join("patch-1.MPQ");
+        ArchiveBuilder::new()
+            .version(FormatVersion::V1)
+            .add_file_data(spell.to_vec(), r"DBFilesClient\Spell.dbc")
+            .build(&archive)
+            .unwrap();
+        crate::vanilla_mpq::normalize(&archive).unwrap();
+        assert!(russian_archives(temp.path())
+            .unwrap_err()
+            .to_string()
+            .contains("5875 layout"));
+    }
+
+    #[test]
+    fn rejecting_an_output_inside_an_input_creates_no_directories() {
+        let temp = tempfile::tempdir().unwrap();
+        let input = temp.path().join("install");
+        fs::create_dir(&input).unwrap();
+        assert!(ensure_outside(&input, &input.join("scratch/out")).is_err());
+        assert!(!input.join("scratch").exists());
+        let outside = temp.path().join("new-parent/out");
+        ensure_outside(&input, &outside).unwrap();
+        assert!(
+            !outside.parent().unwrap().exists(),
+            "validation is read-only"
+        );
+    }
 }
diff --git a/docs/MAP.md b/docs/MAP.md
index c88704079..54abb1ff8 100644
--- a/docs/MAP.md
+++ b/docs/MAP.md
@@ -106,7 +106,7 @@
 - **benilla-adt** (lib.rs): combined_alpha 
 - **benilla-app** (lib.rs): addon_harness area area_poi area_trigger asset_churn aura_visual bindings blob_shadow bowstring camera_shake capture char_create char_select chat_bubble chr_classes cinematic combat_log combat_text console crash creature_anim creature_type cursor cvars death debug_panel dev doodad_events entities fishing_line footprints game_plugins game_tip glue glue_strings go_anim go_templates hover_log items loading_screen local_state login minimap name_persist nameplates names net npc_text opaque2d pending_item_ops perf pipe_warm player poi_marker portrait preflight probe_shield query_cache quest_markers raid_marks ranged_flex realm_select realmlist run_mode screen_fade screenshot script_calls shaders shutdown smart_rect sound spell swing_refusal target test_support text_filter text_reshape textinput transport tutorial ui_action ui_auction ui_aura ui_bank ui_battlefield ui_battlefield_positions ui_battlefield_score ui_bind_confirm ui_binder ui_cast ui_char ui_chat ui_craft ui_dialog_verbs ui_dressup ui_duel ui_follow ui_gamma ui_gm_ticket ui_gossip ui_guild ui_honor ui_inspect ui_instance ui_item_text ui_items ui_layout ui_logout ui_loot ui_loot_roll ui_macro ui_mail ui_merchant ui_mirror ui_models ui_net ui_party ui_pass ui_pet ui_pet_book ui_pet_doll ui_pet_stats ui_petition ui_quest ui_quest_log ui_quest_share ui_reputation ui_saved ui_script ui_session ui_shapeshift ui_social ui_spellbook ui_stable ui_summon ui_tabard ui_talent ui_talent_wipe ui_taxi ui_text ui_tooltip ui_trade ui_tradeskill ui_trainer ui_unit ui_world_map video vplates weapon_trail world_backdrop world_state world_state_ui 
 - **benilla-assets** (lib.rs): adt anim_rng blp column_grid coords gpu_blp m2 materials minimap_grid model spatial_cache terrain tex_filter trace wdt wmo world_assets 
-- **benilla-formats** (lib.rs): anim_data area_poi area_sound area_table area_trigger auction_house bank_bag_slot_prices camera_shakes cfg_categories cfg_configs chain characters chat_channels chr_classes cinematics creature_families creature_sound creature_types creatures dbc death_thud durability elevators emit_timing emote_text emotes environmental_damage exhaustion factions footsteps game_tips gameobjects garble gm_ticket_category ground_effects install item_random_properties item_sounds item_visuals itembagfamily itemclass items itemsets itemsubclass languages light liquid loading_screen lock lock_type macro_icons maps material minimap_translate models npc_greeting packages page_text_material particles pet_stats quest_headers quest_info race_creature_type race_pvp_team race_sound ribbons server_messages sheathe skill_lines sound_entries sound_provider sound_water spell_focus spell_mechanic spell_visual spells stable_slot_prices stationery talents taxi taxi_nodes taxi_path terrain text_filter_lists tga transport_period transports unit_blood value_track vocal_ui_sounds wdl weapon_impact weapon_swing wmo_area world_map_area world_map_continent world_map_overlay world_state_ui wow_ini zone_map 
+- **benilla-formats** (lib.rs): anim_data area_poi area_sound area_table area_trigger auction_house bank_bag_slot_prices camera_shakes cfg_categories cfg_configs chain characters chat_channels chr_classes cinematics creature_families creature_sound creature_types creatures dbc death_thud durability elevators emit_timing emote_text emotes environmental_damage exhaustion factions footsteps game_tips gameobjects garble gm_ticket_category ground_effects install item_random_properties item_sounds item_visuals itembagfamily itemclass items itemsets itemsubclass languages light liquid loading_screen locale lock lock_type macro_icons maps material minimap_translate models npc_greeting packages page_text_material particles pet_stats quest_headers quest_info race_creature_type race_pvp_team race_sound ribbons server_messages sheathe skill_lines sound_entries sound_provider sound_water spell_focus spell_mechanic spell_visual spells stable_slot_prices stationery talents taxi taxi_nodes taxi_path terrain text_filter_lists tga transport_period transports unit_blood value_track vocal_ui_sounds wdl weapon_impact weapon_swing wmo_area world_map_area world_map_continent world_map_overlay world_state_ui wow_ini zone_map 
 - **benilla-m2** (lib.rs): error model skin tests track 
 - **benilla-mpq** (lib.rs): crypto 
 - **benilla-protocol** (lib.rs): auth events guid messages wire world 
@@ -304,6 +304,7 @@
 - `WOW_LIVE_SHOT_AT` — benilla-app/src/capture/live_shot.rs
 - `WOW_LIVE_SHOT_COUNT` — benilla-app/src/capture/live_shot.rs
 - `WOW_LIVE_SHOT_EVERY` — benilla-app/src/capture/live_shot.rs
+- `WOW_LOCALE` — benilla-formats/src/locale.rs
 - `WOW_LOGIN_SHOT` — benilla-world/src/bgwin.rs
 - `WOW_LOGIN_SHOT_OUT` — benilla-app/src/login/screen.rs
 - `WOW_LOGIN_SMOKE` — benilla-app/src/char_select/mod.rs, benilla-app/src/login/mod.rs, benilla-app/src/login/smoke.rs, benilla-world/src/bgwin.rs