feat(desktop): add Arabic (ar) locale with RTL support

Arabic is the desktop app's first right-to-left locale. The i18n provider
now sets `document.dir`/`lang` from the active locale so Tailwind logical
utilities flip automatically, and `ar` is registered in the catalog,
language options, and alias table. The catalog is a partial `defineLocale`
so keys added to English later fall back cleanly.

Co-authored-by: 3ssiri <assiri@gmail.com>
Co-authored-by: Da7-Tech <286182457+Da7-Tech@users.noreply.github.com>

apps/desktop/src/i18n/catalog.ts

@@ -1,3 +1,4 @@
+import { ar } from './ar'
 import { en } from './en'
 import { ja } from './ja'
 import type { Locale, Translations } from './types'
@@ -8,5 +9,6 @@ export const TRANSLATIONS: Record<Locale, Translations> = {
   en,
   zh,
   'zh-hant': zhHant,
-  ja
+  ja,
+  ar
 }

apps/desktop/src/i18n/context.test.tsx

@@ -209,6 +209,24 @@ describe('I18nProvider', () => {
     expect(screen.getByTestId('locale').textContent).toBe('ja')
   })
 
+  it('applies RTL direction for Arabic and restores LTR on switch back', async () => {
+    render(
+      <I18nProvider configClient={null} initialLocale="ar">
+        <LanguageProbe target="en" />
+      </I18nProvider>
+    )
+
+    expect(screen.getByTestId('locale').textContent).toBe('ar')
+    expect(document.documentElement.dir).toBe('rtl')
+    expect(document.documentElement.lang).toBe('ar')
+
+    fireEvent.click(screen.getByRole('button', { name: 'switch' }))
+
+    await waitFor(() => expect(screen.getByTestId('locale').textContent).toBe('en'))
+    expect(document.documentElement.dir).toBe('ltr')
+    expect(document.documentElement.lang).toBe('en')
+  })
+
   it('rolls back the visible locale when saving fails', async () => {
     const configClient: I18nConfigClient = {
       getConfig: vi.fn().mockResolvedValue({ display: { language: 'en' } }),

apps/desktop/src/i18n/context.tsx

@@ -55,6 +55,17 @@ function toError(error: unknown): Error {
   return error instanceof Error ? error : new Error(String(error))
 }
 
+const RTL_LOCALES = new Set<Locale>(['ar'])
+
+function applyDocumentLocale(locale: Locale) {
+  if (typeof document === 'undefined') {
+    return
+  }
+
+  document.documentElement.lang = locale
+  document.documentElement.dir = RTL_LOCALES.has(locale) ? 'rtl' : 'ltr'
+}
+
 export interface I18nContextValue {
   configLoadError: Error | null
   isLoadingConfig: boolean
@@ -92,6 +103,7 @@ export function I18nProvider({ children, configClient = defaultConfigClient, ini
   useEffect(() => {
     localeRef.current = locale
     setRuntimeI18nLocale(locale)
+    applyDocumentLocale(locale)
   }, [locale])
 
   useEffect(() => {

apps/desktop/src/i18n/languages.test.ts

@@ -15,6 +15,9 @@ describe('desktop i18n languages', () => {
     expect(normalizeLocale('zh_HK')).toBe('zh-hant')
     expect(normalizeLocale('ja')).toBe('ja')
     expect(normalizeLocale('ja-JP')).toBe('ja')
+    expect(normalizeLocale('ar')).toBe('ar')
+    expect(normalizeLocale('AR-SA')).toBe('ar')
+    expect(normalizeLocale(' ar_eg ')).toBe('ar')
   })
 
   it('falls back to English for empty or unsupported values', () => {
@@ -32,6 +35,7 @@ describe('desktop i18n languages', () => {
     expect(isLocale('zh')).toBe(true)
     expect(isLocale('zh-hant')).toBe(true)
     expect(isLocale('ja')).toBe(true)
+    expect(isLocale('ar')).toBe(true)
   })
 
   it('returns the persisted config value for supported locales', () => {
@@ -39,5 +43,6 @@ describe('desktop i18n languages', () => {
     expect(localeConfigValue('zh')).toBe('zh')
     expect(localeConfigValue('zh-hant')).toBe('zh-hant')
     expect(localeConfigValue('ja')).toBe('ja')
+    expect(localeConfigValue('ar')).toBe('ar')
   })
 })

apps/desktop/src/i18n/languages.ts

@@ -28,6 +28,12 @@ export const LOCALE_OPTIONS = [
     name: '日本語',
     englishName: 'Japanese',
     configValue: 'ja'
+  },
+  {
+    id: 'ar',
+    name: 'العربية',
+    englishName: 'Arabic',
+    configValue: 'ar'
   }
 ] as const satisfies readonly { configValue: string; englishName: string; id: Locale; name: string }[]
 
@@ -64,7 +70,16 @@ const LOCALE_ALIASES: Record<string, Locale> = {
   zh_hant_hk: 'zh-hant',
   ja: 'ja',
   'ja-jp': 'ja',
-  ja_jp: 'ja'
+  ja_jp: 'ja',
+  ar: 'ar',
+  'ar-sa': 'ar',
+  ar_sa: 'ar',
+  'ar-ae': 'ar',
+  ar_ae: 'ar',
+  'ar-eg': 'ar',
+  ar_eg: 'ar',
+  arabic: 'ar',
+  العربية: 'ar'
 }
 
 export function isLocale(value: unknown): value is Locale {

apps/desktop/src/i18n/types.ts

@@ -5,7 +5,7 @@
 // partial locales should use `defineLocale()` so missing desktop-only strings
 // fall back to English while new keys remain type-checked.
 
-export type Locale = 'en' | 'zh' | 'zh-hant' | 'ja'
+export type Locale = 'en' | 'zh' | 'zh-hant' | 'ja' | 'ar'
 
 export type ToolTitleKey =
   | 'browser_click'