fix(frontend): 修复静态导出下切换语言无效的问题

docs/changelog/index.md

@@ -16,6 +16,7 @@ sidebar: false
 ### 🛠 修复
 - 修复自定义 Webhook 推送在企业微信/钉钉返回 HTTP 200 但 `errcode` 非零时仍记为成功的问题；任务日志会记录上游响应体。
 - 修复 OpenTelemetry Resource 绑定 semconv schema 版本导致 SDK 升级后可能无法启动的问题。
+- 修复静态导出（build:embed）部署下切换语言无效的问题：此前页面在构建时固定为默认中文，运行时不再读取 `NEXT_LOCALE`；现在客户端会按 cookie/浏览器语言重新解析并切换界面语言与 `html lang`。
 
 ### 💄 其他/体验
 - 前端使用 `next/font` 自托管 Inter，并忽略浏览器扩展改写 `body` 属性引起的 hydration 警告。

frontend/components/providers/intl-provider.test.tsx

@@ -0,0 +1,73 @@
+import { render, screen } from '@testing-library/react';
+import { useTranslations } from 'next-intl';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+
+import enMessages from '@/messages/en.json';
+import zhCNMessages from '@/messages/zh-CN.json';
+
+import { AppIntlProvider } from './intl-provider';
+
+function Probe() {
+  const t = useTranslations('common');
+  return <button>{t('save')}</button>;
+}
+
+const zhSave = (zhCNMessages.common as Record<string, string>).save;
+const enSave = (enMessages.common as Record<string, string>).save;
+
+describe('AppIntlProvider (static export locale resolution)', () => {
+  beforeEach(() => {
+    // Deterministic browser language (jsdom defaults to en-US).
+    Object.defineProperty(navigator, 'languages', {
+      value: ['zh-CN'],
+      configurable: true,
+    });
+    Object.defineProperty(navigator, 'language', {
+      value: 'zh-CN',
+      configurable: true,
+    });
+    document.documentElement.lang = 'zh-CN'; // as pre-rendered by SSR
+  });
+
+  afterEach(() => {
+    document.cookie = 'NEXT_LOCALE=; Max-Age=0; Path=/';
+  });
+
+  it('flips to the NEXT_LOCALE cookie locale after mount when SSR locale is stale', async () => {
+    // Static export pre-renders with the build-time default (zh-CN) even when
+    // the user previously chose en — the exact reported bug.
+    document.cookie = 'NEXT_LOCALE=en; Path=/';
+
+    render(
+      <AppIntlProvider locale="zh-CN" messages={zhCNMessages}>
+        <Probe />
+      </AppIntlProvider>,
+    );
+
+    expect(await screen.findByText(enSave)).toBeInTheDocument();
+    expect(document.documentElement.lang).toBe('en');
+  });
+
+  it('keeps the SSR locale when the cookie matches it', () => {
+    document.cookie = 'NEXT_LOCALE=zh-CN; Path=/';
+
+    render(
+      <AppIntlProvider locale="zh-CN" messages={zhCNMessages}>
+        <Probe />
+      </AppIntlProvider>,
+    );
+
+    expect(screen.getByText(zhSave)).toBeInTheDocument();
+    expect(document.documentElement.lang).toBe('zh-CN');
+  });
+
+  it('does not flip without a cookie preference', () => {
+    render(
+      <AppIntlProvider locale="zh-CN" messages={zhCNMessages}>
+        <Probe />
+      </AppIntlProvider>,
+    );
+
+    expect(screen.getByText(zhSave)).toBeInTheDocument();
+  });
+});

frontend/components/providers/intl-provider.tsx

@@ -1,9 +1,18 @@
 'use client';
 
+import { useEffect, useState } from 'react';
 import { NextIntlClientProvider } from 'next-intl';
 import type { AbstractIntlMessages } from 'next-intl';
 import type { ReactNode } from 'react';
+import { resolveClientLocale } from '@/i18n/client';
 import type { AppLocale } from '@/i18n/config';
+import enMessages from '@/messages/en.json';
+import zhCNMessages from '@/messages/zh-CN.json';
+
+const messagesByLocale: Record<AppLocale, AbstractIntlMessages> = {
+  'zh-CN': zhCNMessages,
+  en: enMessages,
+};
 
 type Props = {
   locale: AppLocale;
@@ -11,11 +20,33 @@ type Props = {
   children: ReactNode;
 };
 
-export function AppIntlProvider({ locale, messages, children }: Props) {
+export function AppIntlProvider({
+  locale: ssrLocale,
+  messages: ssrMessages,
+  children,
+}: Props) {
+  // Static export (NEXT_STANDALONE_EXPORT) pre-renders every page at build time
+  // with the default locale, so the SSR locale is stale at runtime. Re-resolve
+  // from the NEXT_LOCALE cookie / browser language on the client. The first
+  // render stays identical to SSR to avoid a hydration mismatch, then flips —
+  // the brief flash matches the theme-hydration pattern (suppressHydrationWarning
+  // is already set on <html>/<body>).
+  const [clientLocale, setClientLocale] = useState<AppLocale | null>(null);
+
+  useEffect(() => {
+    const resolved = resolveClientLocale();
+    if (resolved !== ssrLocale) {
+      setClientLocale(resolved);
+      document.documentElement.lang = resolved;
+    }
+  }, [ssrLocale]);
+
+  const locale = clientLocale ?? ssrLocale;
+
   return (
     <NextIntlClientProvider
       locale={locale}
-      messages={messages}
+      messages={clientLocale ? messagesByLocale[clientLocale] : ssrMessages}
       timeZone='Asia/Shanghai'
     >
       {children}