Added language and theme switching function to login page and homepage

lightrag_webui/src/components/LanguageToggle.tsx

@@ -0,0 +1,49 @@
+import Button from '@/components/ui/Button'
+import { useCallback } from 'react'
+import { controlButtonVariant } from '@/lib/constants'
+import { useTranslation } from 'react-i18next'
+import { useSettingsStore } from '@/stores/settings'
+
+/**
+ * Component that toggles the language between English and Chinese.
+ */
+export default function LanguageToggle() {
+  const { i18n } = useTranslation()
+  const currentLanguage = i18n.language
+  const setLanguage = useSettingsStore.use.setLanguage()
+
+  const setEnglish = useCallback(() => {
+    i18n.changeLanguage('en')
+    setLanguage('en')
+  }, [i18n, setLanguage])
+
+  const setChinese = useCallback(() => {
+    i18n.changeLanguage('zh')
+    setLanguage('zh')
+  }, [i18n, setLanguage])
+
+  if (currentLanguage === 'zh') {
+    return (
+      <Button
+        onClick={setEnglish}
+        variant={controlButtonVariant}
+        tooltip="Switch to English"
+        size="icon"
+        side="bottom"
+      >
+        中
+      </Button>
+    )
+  }
+  return (
+    <Button
+      onClick={setChinese}
+      variant={controlButtonVariant}
+      tooltip="切换到中文"
+      size="icon"
+      side="bottom"
+    >
+      EN
+    </Button>
+  )
+}