feat: integrate language switcher into settings with modern segment control UI

- Move language switcher from header to settings modal for better organization
- Implement modern segment control UI instead of radio buttons for language selection
- Add language preference persistence in localStorage and backend settings
- Support instant language preview with cancel/revert functionality
- Remove standalone LanguageSwitcher component
- Improve initial language detection logic (localStorage -> browser -> default)
- Add proper i18n keys for language settings UI text

src/i18n/index.ts

@@ -4,6 +4,36 @@ import { initReactI18next } from "react-i18next";
 import en from "./locales/en.json";
 import zh from "./locales/zh.json";
 
+const DEFAULT_LANGUAGE: "zh" | "en" = "zh";
+
+const getInitialLanguage = (): "zh" | "en" => {
+  if (typeof window !== "undefined") {
+    try {
+      const stored = window.localStorage.getItem("language");
+      if (stored === "zh" || stored === "en") {
+        return stored;
+      }
+    } catch (error) {
+      console.warn("[i18n] Failed to read stored language preference", error);
+    }
+  }
+
+  const navigatorLang =
+    typeof navigator !== "undefined"
+      ? navigator.language?.toLowerCase() ?? navigator.languages?.[0]?.toLowerCase()
+      : undefined;
+
+  if (navigatorLang?.startsWith("zh")) {
+    return "zh";
+  }
+
+  if (navigatorLang?.startsWith("en")) {
+    return "en";
+  }
+
+  return DEFAULT_LANGUAGE;
+};
+
 const resources = {
   en: {
     translation: en,
@@ -15,7 +45,7 @@ const resources = {
 
 i18n.use(initReactI18next).init({
   resources,
-  lng: "zh", // 默认语言调整为中文
+  lng: getInitialLanguage(), // 根据本地存储或系统语言选择默认语言
   fallbackLng: "en", // 如果缺少中文翻译则退回英文
 
   interpolation: {

src/i18n/locales/en.json

@@ -62,6 +62,11 @@
   },
   "settings": {
     "title": "Settings",
+    "general": "General",
+    "language": "Language",
+    "languageDescription": "Choose the display language for CC Switch. This preference will be remembered next time you open the app.",
+    "languageOptionChinese": "中文",
+    "languageOptionEnglish": "English",
     "windowBehavior": "Window Behavior",
     "minimizeToTray": "Minimize to tray on close",
     "minimizeToTrayDescription": "When checked, clicking the close button will hide to system tray, otherwise the app will exit directly.",

src/i18n/locales/zh.json

@@ -62,6 +62,11 @@
   },
   "settings": {
     "title": "设置",
+    "general": "通用",
+    "language": "界面语言",
+    "languageDescription": "选择 CC Switch 的显示语言，下次启动会自动记住你的偏好。",
+    "languageOptionChinese": "中文",
+    "languageOptionEnglish": "English",
     "windowBehavior": "窗口行为",
     "minimizeToTray": "关闭时最小化到托盘",
     "minimizeToTrayDescription": "勾选后点击关闭按钮会隐藏到系统托盘，取消则直接退出应用。",