The language-data library currently provides getLanguagesInTerritory, but the API does not expose a way to retrieve the full list of supported territories. As a result, consumers cannot easily discover all territories and the languages associated with them.

We should add a method that returns territory-based language information, including a way to enumerate all available territories. This should be implemented in both the PHP and JavaScript APIs.

After this change is completed, we should publish a new release of the language-data library.

Relevant existing API: LanguageUtil::getLanguagesInTerritory

Acceptance criteria

• A new API method is added to the library to return the list of supported territories.
• The new functionality is available in both the PHP and JavaScript APIs.
• The public documentation is updated:
• https://language-data.readthedocs.io/en/latest/api/languagedata/languageutil.html#LanguageUtil::getTerritoriesWithLanguages
• Existing API behavior remains unchanged.
• A new library release is created after the change is merged.

QA plan

• Use this code in the new content language selector
• https://gerrit.wikimedia.org/r/c/mediawiki/extensions/UniversalLanguageSelector/+/1271003
• Confirm docs are correct