feat: add response language selector in General settings

Expose the CLI's `language` setting in the desktop app's General tab.
Users can now pick from 21 pre-defined languages via a dropdown (value
maps directly to CLI language names such as "chinese", "japanese").
Selecting a language writes it to ~/.claude/settings.json so the CLI
injects the language instruction into every session's system prompt.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

desktop/src/i18n/locales/en.ts

@@ -643,6 +643,9 @@ export const en = {
   'settings.general.appearance.dark': 'Dark',
   'settings.general.languageTitle': 'Language',
   'settings.general.languageDescription': 'Choose the display language for the application.',
+  'settings.general.responseLangTitle': 'Response Language',
+  'settings.general.responseLangDescription': 'Instruct Claude to always respond in a specific language.',
+  'settings.general.responseLangDefault': 'Default (English)',
   'settings.general.effortTitle': 'Effort Level',
   'settings.general.effortDescription': 'Controls how much computation the model uses.',
   'settings.general.effort.low': 'Low',

desktop/src/i18n/locales/zh.ts

@@ -645,6 +645,9 @@ export const zh: Record<TranslationKey, string> = {
   'settings.general.appearance.dark': '暗色',
   'settings.general.languageTitle': '语言',
   'settings.general.languageDescription': '选择应用程序的显示语言。',
+  'settings.general.responseLangTitle': '回复语言',
+  'settings.general.responseLangDescription': '指定 Claude 始终以某种语言回复。',
+  'settings.general.responseLangDefault': '默认（英语）',
   'settings.general.effortTitle': '推理强度',
   'settings.general.effortDescription': '控制模型使用的计算量。',
   'settings.general.effort.low': '低',

desktop/src/pages/Settings.tsx

@@ -1355,6 +1355,8 @@ function GeneralSettings() {
     setDesktopNotificationsEnabled,
     webSearch,
     setWebSearch,
+    responseLanguage,
+    setResponseLanguage,
   } = useSettingsStore()
   const t = useTranslation()
   const [webSearchDraft, setWebSearchDraft] = useState(webSearch)
@@ -1388,6 +1390,31 @@ function GeneralSettings() {
     { value: 'zh', label: '中文' },
   ]
 
+  const RESPONSE_LANGUAGES: Array<{ value: string; label: string }> = [
+    { value: '', label: t('settings.general.responseLangDefault') },
+    { value: 'english', label: 'English' },
+    { value: 'chinese', label: '中文 (Chinese)' },
+    { value: 'japanese', label: '日本語 (Japanese)' },
+    { value: 'korean', label: '한국어 (Korean)' },
+    { value: 'spanish', label: 'Español (Spanish)' },
+    { value: 'french', label: 'Français (French)' },
+    { value: 'german', label: 'Deutsch (German)' },
+    { value: 'portuguese', label: 'Português (Portuguese)' },
+    { value: 'italian', label: 'Italiano (Italian)' },
+    { value: 'russian', label: 'Русский (Russian)' },
+    { value: 'dutch', label: 'Nederlands (Dutch)' },
+    { value: 'polish', label: 'Polski (Polish)' },
+    { value: 'turkish', label: 'Türkçe (Turkish)' },
+    { value: 'hindi', label: 'हिन्दी (Hindi)' },
+    { value: 'indonesian', label: 'Bahasa Indonesia' },
+    { value: 'ukrainian', label: 'Українська (Ukrainian)' },
+    { value: 'greek', label: 'Ελληνικά (Greek)' },
+    { value: 'czech', label: 'Čeština (Czech)' },
+    { value: 'danish', label: 'Dansk (Danish)' },
+    { value: 'swedish', label: 'Svenska (Swedish)' },
+    { value: 'norwegian', label: 'Norsk (Norwegian)' },
+  ]
+
   const THEMES: Array<{ value: ThemeMode; label: string }> = [
     { value: 'light', label: t('settings.general.appearance.light') },
     { value: 'dark', label: t('settings.general.appearance.dark') },
@@ -1493,6 +1520,21 @@ function GeneralSettings() {
         ))}
       </div>
 
+      {/* Response Language */}
+      <h2 className="text-base font-semibold text-[var(--color-text-primary)] mb-1">{t('settings.general.responseLangTitle')}</h2>
+      <p className="text-sm text-[var(--color-text-tertiary)] mb-3">{t('settings.general.responseLangDescription')}</p>
+      <div className="flex gap-2 mb-8">
+        <select
+          value={responseLangDraft}
+          onChange={(e) => void setResponseLanguage(e.target.value)}
+          className="flex-1 px-3 py-2 text-sm rounded-lg border border-[var(--color-border)] bg-[var(--color-surface-container-low)] text-[var(--color-text-primary)] focus:outline-none focus:border-[var(--color-brand)] transition-colors cursor-pointer"
+        >
+          {RESPONSE_LANGUAGES.map(({ value, label }) => (
+            <option key={value} value={value}>{label}</option>
+          ))}
+        </select>
+      </div>
+
       {/* Effort Level */}
       <h2 className="text-base font-semibold text-[var(--color-text-primary)] mb-1">{t('settings.general.effortTitle')}</h2>
       <p className="text-sm text-[var(--color-text-tertiary)] mb-3">{t('settings.general.effortDescription')}</p>

desktop/src/stores/settingsStore.ts

@@ -28,6 +28,7 @@ type SettingsStore = {
   skipWebFetchPreflight: boolean
   desktopNotificationsEnabled: boolean
   webSearch: WebSearchSettings
+  responseLanguage: string
   isLoading: boolean
   error: string | null
 
@@ -41,6 +42,7 @@ type SettingsStore = {
   setSkipWebFetchPreflight: (enabled: boolean) => Promise<void>
   setDesktopNotificationsEnabled: (enabled: boolean) => Promise<void>
   setWebSearch: (settings: WebSearchSettings) => Promise<void>
+  setResponseLanguage: (language: string) => Promise<void>
 }
 
 export const useSettingsStore = create<SettingsStore>((set, get) => ({
@@ -55,6 +57,7 @@ export const useSettingsStore = create<SettingsStore>((set, get) => ({
   skipWebFetchPreflight: true,
   desktopNotificationsEnabled: false,
   webSearch: { mode: 'auto', tavilyApiKey: '', braveApiKey: '' },
+  responseLanguage: '',
   isLoading: false,
   error: null,
 
@@ -81,6 +84,7 @@ export const useSettingsStore = create<SettingsStore>((set, get) => ({
         skipWebFetchPreflight: userSettings.skipWebFetchPreflight !== false,
         desktopNotificationsEnabled: userSettings.desktopNotificationsEnabled === true,
         webSearch: normalizeWebSearchSettings(userSettings.webSearch),
+        responseLanguage: typeof userSettings.language === 'string' ? userSettings.language : '',
         isLoading: false,
         error: null,
       })
@@ -186,6 +190,16 @@ export const useSettingsStore = create<SettingsStore>((set, get) => ({
       set({ webSearch: prev })
     }
   },
+
+  setResponseLanguage: async (language) => {
+    const prev = get().responseLanguage
+    set({ responseLanguage: language })
+    try {
+      await settingsApi.updateUser({ language: language || undefined })
+    } catch {
+      set({ responseLanguage: prev })
+    }
+  },
 }))
 
 function normalizeWebSearchSettings(settings: WebSearchSettings | undefined): WebSearchSettings {

desktop/src/types/settings.ts

@@ -29,5 +29,6 @@ export type UserSettings = {
   skipWebFetchPreflight?: boolean
   desktopNotificationsEnabled?: boolean
   webSearch?: WebSearchSettings
+  language?: string
   [key: string]: unknown
 }