Detect locale with is-china-user and show English copy for non-Chinese visitors.

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

components/locale-provider.tsx

@@ -0,0 +1,75 @@
+"use client";
+
+import {
+  createContext,
+  useContext,
+  useEffect,
+  useMemo,
+  useState,
+  type ReactNode,
+} from "react";
+import { isChinaUser } from "is-china-user";
+import { dictionaries, type Dictionary, type Locale } from "~/lib/i18n";
+
+type LocaleContextValue = {
+  locale: Locale;
+  isChina: boolean;
+  ready: boolean;
+  t: Dictionary;
+};
+
+const LocaleContext = createContext<LocaleContextValue | null>(null);
+
+export function LocaleProvider({ children }: { children: ReactNode }) {
+  // Default zh to match primary audience; switch after client detection.
+  const [locale, setLocale] = useState<Locale>("zh");
+  const [ready, setReady] = useState(false);
+
+  useEffect(() => {
+    let cancelled = false;
+
+    try {
+      const china = Boolean(isChinaUser());
+      if (!cancelled) {
+        setLocale(china ? "zh" : "en");
+        setReady(true);
+      }
+    } catch {
+      if (!cancelled) {
+        setLocale("zh");
+        setReady(true);
+      }
+    }
+
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  useEffect(() => {
+    if (!ready) return;
+    document.documentElement.lang = dictionaries[locale].htmlLang;
+  }, [locale, ready]);
+
+  const value = useMemo<LocaleContextValue>(
+    () => ({
+      locale,
+      isChina: locale === "zh",
+      ready,
+      t: dictionaries[locale],
+    }),
+    [locale, ready],
+  );
+
+  return (
+    <LocaleContext.Provider value={value}>{children}</LocaleContext.Provider>
+  );
+}
+
+export function useLocale() {
+  const ctx = useContext(LocaleContext);
+  if (!ctx) {
+    throw new Error("useLocale must be used within LocaleProvider");
+  }
+  return ctx;
+}