feat(i18n): add Traditional Chinese (zh-TW) locale support

Add full Traditional Chinese (繁體中文) support to the client UI.

- Create `zh-TW.ts` translation file (converted from zh-CN via OpenCC s2twp)
- Register zh-TW resource in i18next init
- Extend Locale type to include "zh-TW"
- Auto-detect zh-TW/zh-HK browser locale
- Add "繁體中文" option to language switcher and settings page
- Update desktop renderer i18n helper with zh-TW fallback

Closes #1120

Made-with: Cursor

Author: caiqiling958-cmd

apps/desktop/src/lib/i18n.ts

@@ -10,9 +10,19 @@
 /**
  * Returns the locale-appropriate string set based on `navigator.language`.
  * Falls back to English for any non-Chinese locale.
+ * When `zh-TW` or `zh-HK` is detected and a `"zh-TW"` key exists, it is
+ * preferred; otherwise falls back to `zh`.
  *
  * `en` and `zh` must share the same structural shape — string values may differ.
  */
-export function resolveLocale<T>(strings: { en: T; zh: T }): T {
-  return navigator.language.startsWith("zh") ? strings.zh : strings.en;
+export function resolveLocale<T>(strings: {
+  en: T;
+  zh: T;
+  "zh-TW"?: T;
+}): T {
+  const lang = navigator.language;
+  if (lang === "zh-TW" || lang === "zh-HK") {
+    return strings["zh-TW"] ?? strings.zh;
+  }
+  return lang.startsWith("zh") ? strings.zh : strings.en;
 }

apps/web/src/components/language-switcher.tsx

@@ -38,7 +38,8 @@ export function LanguageSwitcher({ variant = "light", size = "sm" }: Props) {
 
   const options: Array<{ value: Locale; label: string }> = [
     { value: "en", label: "English" },
-    { value: "zh", label: "中文" },
+    { value: "zh", label: "简体中文" },
+    { value: "zh-TW", label: "繁體中文" },
   ];
 
   const currentLabel =

apps/web/src/hooks/use-locale.tsx

@@ -13,7 +13,7 @@ import {
   patchApiInternalDesktopPreferences,
 } from "../../lib/api/sdk.gen";
 
-export type Locale = "en" | "zh";
+export type Locale = "en" | "zh" | "zh-TW";
 
 interface LocaleCtx {
   locale: Locale;
@@ -26,12 +26,15 @@ const STORAGE_KEY = "nexu_locale";
 function detectDefault(): Locale {
   try {
     const stored = localStorage.getItem(STORAGE_KEY);
-    if (stored === "en" || stored === "zh") return stored;
+    if (stored === "en" || stored === "zh" || stored === "zh-TW")
+      return stored;
   } catch {
     /* ignore */
   }
   const lang = navigator.language || "";
-  return lang.startsWith("zh") ? "zh" : "en";
+  if (lang === "zh-TW" || lang === "zh-HK") return "zh-TW";
+  if (lang.startsWith("zh")) return "zh";
+  return "en";
 }
 
 const LocaleContext = createContext<LocaleCtx>({
@@ -49,7 +52,12 @@ export function LocaleProvider({ children }: { children: ReactNode }) {
   const userInteractedRef = useRef(false);
 
   useEffect(() => {
-    document.documentElement.lang = locale === "zh" ? "zh-CN" : "en";
+    const langMap: Record<Locale, string> = {
+      en: "en",
+      zh: "zh-CN",
+      "zh-TW": "zh-TW",
+    };
+    document.documentElement.lang = langMap[locale];
   }, [locale]);
 
   useEffect(() => {
@@ -92,9 +100,14 @@ export function useLocale() {
 }
 
 async function syncDesktopLocale(locale: Locale): Promise<void> {
+  const apiLocaleMap: Record<Locale, string> = {
+    en: "en",
+    zh: "zh-CN",
+    "zh-TW": "zh-TW",
+  };
   await patchApiInternalDesktopPreferences({
     body: {
-      locale: locale === "zh" ? "zh-CN" : "en",
+      locale: apiLocaleMap[locale],
     },
   }).catch(() => {
     // Best-effort sync only; local UI language should still work offline.
@@ -118,8 +131,17 @@ async function bootstrapLocale(
     return;
   }
 
-  if (storedLocale === "en" || storedLocale === "zh-CN") {
-    const nextLocale = storedLocale === "zh-CN" ? "zh" : "en";
+  if (
+    storedLocale === "en" ||
+    storedLocale === "zh-CN" ||
+    storedLocale === "zh-TW"
+  ) {
+    const nextLocale: Locale =
+      storedLocale === "zh-CN"
+        ? "zh"
+        : storedLocale === "zh-TW"
+          ? "zh-TW"
+          : "en";
     await i18n.changeLanguage(nextLocale);
     setLocaleState(nextLocale);
     try {

apps/web/src/i18n/index.ts

@@ -2,24 +2,28 @@ import i18n from "i18next";
 import { initReactI18next } from "react-i18next";
 import en from "./locales/en";
 import zhCN from "./locales/zh-CN";
+import zhTW from "./locales/zh-TW";
 
 const STORAGE_KEY = "nexu_locale";
 
 function detectLocale(): string {
   try {
     const stored = localStorage.getItem(STORAGE_KEY);
-    if (stored === "en" || stored === "zh") return stored;
+    if (stored === "en" || stored === "zh" || stored === "zh-TW") return stored;
   } catch {
     /* ignore */
   }
   const lang = navigator.language || "";
-  return lang.startsWith("zh") ? "zh" : "en";
+  if (lang === "zh-TW" || lang === "zh-HK") return "zh-TW";
+  if (lang.startsWith("zh")) return "zh";
+  return "en";
 }
 
 i18n.use(initReactI18next).init({
   resources: {
     en: { translation: en },
     zh: { translation: zhCN },
+    "zh-TW": { translation: zhTW },
   },
   lng: detectLocale(),
   fallbackLng: "en",