feat: close #2618 use correct html lang attr

app/components/home.tsx

@@ -15,7 +15,7 @@ import dynamic from "next/dynamic";
 import { Path, SlotID } from "../constant";
 import { ErrorBoundary } from "./error";
 
-import { getLang } from "../locales";
+import { getISOLang, getLang } from "../locales";
 
 import {
   HashRouter as Router,
@@ -86,6 +86,17 @@ export function useSwitchTheme() {
   }, [config.theme]);
 }
 
+function useHtmlLang() {
+  useEffect(() => {
+    const lang = getISOLang();
+    const htmlLang = document.documentElement.lang;
+
+    if (lang !== htmlLang) {
+      document.documentElement.lang = lang;
+    }
+  }, []);
+}
+
 const useHasHydrated = () => {
   const [hasHydrated, setHasHydrated] = useState<boolean>(false);
 
@@ -168,6 +179,7 @@ export function useLoadData() {
 export function Home() {
   useSwitchTheme();
   useLoadData();
+  useHtmlLang();
 
   useEffect(() => {
     console.log("[Config] got config from build time", getClientConfig());

app/layout.tsx

@@ -3,7 +3,7 @@ import "./styles/globals.scss";
 import "./styles/markdown.scss";
 import "./styles/highlight.scss";
 import { getClientConfig } from "./config/client";
-import { type Metadata } from 'next';
+import { type Metadata } from "next";
 
 export const metadata: Metadata = {
   title: "ChatGPT Next Web",

app/locales/index.ts

@@ -116,3 +116,13 @@ export function changeLang(lang: Lang) {
   setItem(LANG_KEY, lang);
   location.reload();
 }
+
+export function getISOLang() {
+  const isoLangString: Record<string, string> = {
+    cn: "zh-Hans",
+    tw: "zh-Hant",
+  };
+
+  const lang = getLang();
+  return isoLangString[lang] ?? lang;
+}