Vlad Here you go:
Interface Language
To provide a consistent experience for non English speaking users, setting the interface language should also set the default Quick Answer, Summarizer and Assistant output language to the desired locale. The default option should be 'Auto' where Kagi guesses what the output language should be.
Research Assistant
For multi lingual users, it makes sense to be able to change the output language of the research assistant directly in the interface. Thereby some content can be researched in one's mother tongue, while other topics can be processed in one's 2nd or 3rd languages without leaving the assistant interface.
A similar quick setting could be applied to Quick Answer to allow for more flexibility while searching the web.