Steps to replicate the issue (include links if applicable):
Load the system messages for the the language no: https://no.wikipedia.org/wiki/Special:AllMessages?filter=modified&lang=no
What happens?:
It shows the system messages in nb instead of no. Although there is a system message in language no: https://no.wikipedia.org/wiki/MediaWiki:Maintenance-all-question-title/no
What should have happened instead?:
It should show the system messages in the selected language code, even if this is a dummy or a deprecated language code. This allows to detect messages in deprecated language codes.