Steps to replicate the issue (include links if applicable):

• Go to any special page with namespace selector with language variants
  • For example, Special:AllPages: https://zh.wikipedia.org/zh-tw/Special:AllPages
• Test 1: Check the option labels in the namespace selector with JavaScript disabled
• Test 2: Check the option labels in the namespace selector with JavaScript enabled
• Test 3: Try to execute mw.widgets.NamespaceInputWidget.static.getNamespaceDropdownOptions( {} ); in console

What happens?:

• Test 2: The language variant namespace names unexpectedly replaced by canonical namespace names.
• Test 3: The cause (the returned result didn't contain any information about language variant namespace names)
• When JavaScript being enabled, it made the language variant namespace names unexpectedly replaced by canonical namespace names.

What should have happened instead?:

• Test 1: Expected options
• The namespace names should show in the variant, like what it shows without JavaScript
• resources/src/mediawiki.widgets/mw.widgets.NamespacesMultiselectWidget.js should use language variant namespace names instead of changing them to the canonical namespace name
• resources/src/mediawiki.widgets/mw.widgets.NamespaceInputWidget.js#L44 should give information about language variant namespace names

Software version (skip for WMF-hosted wikis like Wikipedia):

• MediaWiki:
  • 1.41.0-alpha ( bb29f22 )
  • 1.42.0-wmf.4 ( de18cff )

Other information (browser name/version, screenshots, etc.):