Feat: Update Chinese language support to use 'zh-cn' as the key and add language configuration

src/i18n/i18n.config.ts

@@ -6,6 +6,6 @@ export default defineI18nConfig(() => ({
   fallbackLocale: 'en',
   messages: {
     en,
-    '简体中文': zh_cn,
+    'zh-cn': zh_cn,
   },
 }));

src/nuxt.config.ts

@@ -31,6 +31,11 @@ export default defineNuxtConfig({
         language: 'en-US',
         name: 'English',
       },
+      {
+        code: 'zh-cn',
+        language: 'zh-CN',
+        name: '简体中文',
+      },
     ],
     defaultLocale: 'en',
     vueI18n: './i18n.config.ts',