Show Chinese locale only when Chinese language signals are detected.

Hide the language switcher for English-only browsers; gate /zh via Accept-Language and a client cookie.

Co-authored-by: Cursor <cursoragent@cursor.com>

components/language-switcher.tsx

@@ -1,8 +1,13 @@
 "use client";
 
+import { useEffect, useMemo, useState } from "react";
 import { useLocale, useTranslations } from "next-intl";
 import { usePathname, useRouter } from "@/i18n/navigation";
-import { routing, type AppLocale } from "@/i18n/routing";
+import type { AppLocale } from "@/i18n/routing";
+import {
+  detectChineseClient,
+  markChineseLocaleAllowed,
+} from "@/lib/chinese-locale";
 import { cn } from "@/lib/utils";
 
 export function LanguageSwitcher() {
@@ -10,6 +15,31 @@ export function LanguageSwitcher() {
   const locale = useLocale() as AppLocale;
   const router = useRouter();
   const pathname = usePathname();
+  const [ready, setReady] = useState(false);
+  const [zhAvailable, setZhAvailable] = useState(false);
+
+  useEffect(() => {
+    const { likely } = detectChineseClient();
+    setZhAvailable(likely);
+    setReady(true);
+
+    if (likely) {
+      markChineseLocaleAllowed();
+    } else if (locale === "zh") {
+      router.replace(pathname, { locale: "en" });
+    }
+  }, [locale, pathname, router]);
+
+  const locales = useMemo(() => {
+    const list: AppLocale[] = ["en"];
+    if (zhAvailable) list.push("zh");
+    return list;
+  }, [zhAvailable]);
+
+  // English-only environments: no language control
+  if (!ready || locales.length < 2) {
+    return null;
+  }
 
   return (
     <div
@@ -17,7 +47,7 @@ export function LanguageSwitcher() {
       role="group"
       aria-label={t("label")}
     >
-      {routing.locales.map((loc) => (
+      {locales.map((loc) => (
         <button
           key={loc}
           type="button"
@@ -28,7 +58,10 @@ export function LanguageSwitcher() {
               : "text-[var(--muted)] hover:text-[var(--ink)]"
           )}
           aria-pressed={loc === locale}
-          onClick={() => router.replace(pathname, { locale: loc })}
+          onClick={() => {
+            if (loc === "zh") markChineseLocaleAllowed();
+            router.replace(pathname, { locale: loc });
+          }}
         >
           {t(loc)}
         </button>