Currently, using a non-existent/incorrect uselang parameter defaults the interface back to en. E.g [1] This is not good/graceful behaviour. Mediawiki should rather first revert to the site's default interface language.
Stumbled upon this while using the hi-wp upload form. One of the links used in the form is [2], which uses the uselang hack to display an appropriate subpage of Mediawiki:Uploadtext to the user per the selected option. However, when the option doesn't exist, Mediawiki defaults back the entire interface to en, which is very inconvenient.
[1]: https://ar.wikipedia.org/?uselang=nonexistent
Version: unspecified
Severity: enhancement