Resolve the language setting persistence issue

- Move i18n initialization to async function
- Sync i18n with settings store language
- Add Root component for i18n loading state
- Convert i18n.js to TypeScript

lightrag_webui/src/i18n.ts

@@ -0,0 +1,37 @@
+import i18n from 'i18next'
+import { initReactI18next } from 'react-i18next'
+import { useSettingsStore } from '@/stores/settings'
+
+import en from './locales/en.json'
+import zh from './locales/zh.json'
+
+// Function to sync i18n with store state
+export const initializeI18n = async (): Promise<typeof i18n> => {
+  // Get initial language from store
+  const initialLanguage = useSettingsStore.getState().language
+
+  // Initialize with store language
+  await i18n.use(initReactI18next).init({
+    resources: {
+      en: { translation: en },
+      zh: { translation: zh }
+    },
+    lng: initialLanguage,
+    fallbackLng: 'en',
+    interpolation: {
+      escapeValue: false
+    }
+  })
+
+  // Subscribe to language changes
+  useSettingsStore.subscribe((state) => {
+    const currentLanguage = state.language
+    if (i18n.language !== currentLanguage) {
+      i18n.changeLanguage(currentLanguage)
+    }
+  })
+
+  return i18n
+}
+
+export default i18n