Language selector incorrectly omits zh-CN after locale change

[whorn07]

Bug Report

Problematic behavior
The application initially loads in Simplified Chinese (zh-CN). However, after switching the language to any other option (e.g., English), the zh-CN option disappears from the language selector, making it impossible to switch back to Simplified Chinese.

Expected behavior/code
The language selector should always display all supported languages—including zh-CN—regardless of the currently selected language, allowing users to freely switch back to Simplified Chinese at any time.

Environment
demo document site

Additional context/Screenshots