The Firefox browser now has a built-in page translator that works even without the Internet::Mozilla has announced the release of an update to its Firefox browser. In version number 118, users will find a significant innovation - a built-in translator
The languages I might want to see aren't necessarily the ones I know. People who are learning languages might set that (I did for the language I'm learning, anyway).
So set whatever you want to see. Am not sure what's your point. That setting tells site which of the languages you'd like to see and if they support it, it should be used. Didn't see any sites use these apart from CMS I wrote.
Maybe I misunderstood you but my point was if it interpreted the language preferences I set in the normal config as "knowing" the languages I added and didn't offer translations, that wouldn't necessarily be what I want.