diff --git a/js/i18n.js b/js/i18n.js
index 8725e92..79b2c2e 100644
--- a/js/i18n.js
+++ b/js/i18n.js
@@ -5,7 +5,7 @@
 
 class I18nManager {
   constructor() {
-    this.currentLang = this.getLanguageFromURL() || 'zh';
+    this.currentLang = this.getInitialLanguage();
     this.translations = {
       zh: {
         title: 'AFX · 支付宝体验技术部 · 引领体验科技，驱动数字生活',
@@ -35,6 +35,59 @@ class I18nManager {
     return urlParams.get('lang');
   }
 
+  /**
+   * 规范化语言值
+   */
+  normalizeLanguage(lang) {
+    if (!lang) {
+      return null;
+    }
+
+    const normalizedLang = lang.toLowerCase();
+
+    if (normalizedLang.startsWith('zh')) {
+      return 'zh';
+    }
+
+    if (normalizedLang.startsWith('en')) {
+      return 'en';
+    }
+
+    return null;
+  }
+
+  /**
+   * 检测浏览器语言
+   */
+  detectBrowserLanguage() {
+    const browserLanguages = navigator.languages?.length
+      ? navigator.languages
+      : [navigator.language];
+
+    for (const lang of browserLanguages) {
+      const normalizedLang = this.normalizeLanguage(lang);
+
+      if (normalizedLang) {
+        return normalizedLang;
+      }
+    }
+
+    return 'en';
+  }
+
+  /**
+   * 获取初始化语言
+   */
+  getInitialLanguage() {
+    const urlLanguage = this.getLanguageFromURL();
+
+    if (urlLanguage !== null) {
+      return this.normalizeLanguage(urlLanguage) || 'en';
+    }
+
+    return this.detectBrowserLanguage();
+  }
+
   /**
    * 更新URL参数
    */
diff --git a/tests/aria-label-i18n.test.mjs b/tests/aria-label-i18n.test.mjs
index 8b6e336..b6a4583 100644
--- a/tests/aria-label-i18n.test.mjs
+++ b/tests/aria-label-i18n.test.mjs
@@ -1,6 +1,7 @@
 import assert from 'node:assert/strict';
 import { readFileSync } from 'node:fs';
 import test from 'node:test';
+import vm from 'node:vm';
 
 const html = readFileSync(new URL('../index.html', import.meta.url), 'utf8');
 const i18nScript = readFileSync(
@@ -27,6 +28,54 @@ function getExternalLinks() {
     .filter(({ attributes }) => attributes.target === '_blank');
 }
 
+function createI18nManager({ search = '', language = 'zh-CN', languages } = {}) {
+  const context = {
+    window: {
+      location: { search },
+      history: { replaceState() {} },
+    },
+    document: {
+      addEventListener() {},
+      getElementById() {
+        return null;
+      },
+      querySelector() {
+        return null;
+      },
+      querySelectorAll() {
+        return [];
+      },
+      dispatchEvent() {},
+      documentElement: { lang: 'zh-CN' },
+    },
+    navigator: {
+      language,
+      languages: languages ?? [language],
+    },
+    URL,
+    URLSearchParams,
+    CustomEvent: class {
+      constructor(type, init) {
+        this.type = type;
+        this.detail = init?.detail;
+      }
+    },
+  };
+
+  vm.createContext(context);
+
+  const i18nScriptWithoutInit = i18nScript.replace(
+    /\n?\s*new I18nManager\(\);\s*$/,
+    ''
+  );
+  vm.runInContext(
+    `${i18nScriptWithoutInit}\nglobalThis.I18nManager = I18nManager;`,
+    context
+  );
+
+  return new context.I18nManager();
+}
+
 test('external links provide localized aria-label values', () => {
   const externalLinks = getExternalLinks();
 
@@ -62,3 +111,39 @@ test('language switch updates localized aria-label values', () => {
   assert.match(i18nScript, /\[data-aria-zh\]\[data-aria-en\]/);
   assert.match(i18nScript, /setAttribute\(\s*['"]aria-label['"]/);
 });
+
+test('defaults to browser English when no lang query is provided', () => {
+  const manager = createI18nManager({ language: 'en-US' });
+
+  assert.equal(manager.currentLang, 'en');
+});
+
+test('defaults to browser Chinese when no lang query is provided', () => {
+  const manager = createI18nManager({ language: 'zh-TW' });
+
+  assert.equal(manager.currentLang, 'zh');
+});
+
+test('valid lang query takes precedence over browser language detection', () => {
+  const manager = createI18nManager({
+    search: '?lang=en',
+    language: 'zh-CN',
+  });
+
+  assert.equal(manager.currentLang, 'en');
+});
+
+test('invalid lang query ignores browser locale and falls back to English', () => {
+  const manager = createI18nManager({
+    search: '?lang=fr',
+    language: 'zh-CN',
+  });
+
+  assert.equal(manager.currentLang, 'en');
+});
+
+test('unrecognized browser language falls back to English', () => {
+  const manager = createI18nManager({ language: 'fr-FR', languages: ['fr-FR'] });
+
+  assert.equal(manager.currentLang, 'en');
+});