Problem is that finding the language from the rolling menu is quite annoying, and as you usually write in language you axpect members of the community would understand, it's easier to left it 'undefined'.

I'm new to Lemmy and on my first day trying to get to grips with it, I couldn't post a comment because the Community wouldn't allow the language (I was posting in English and all the other comments on the post were in English, and my language settings are set to Undefined and English). The whole language selection is actually a blocker to engagement at times.

I personally would like to see posts in 4 languages and as far as I can tell it won't let me specify more than one in my profile so I just leave it on undefined. I'm having I guess the opposite issue to you in that I'm only seeing English content when I would like to see some in my other (non-native) languages for better immersion.

I found that the "language selection" box was bugged on desktop and wouldn't actually apply my settings, but when I tried it on a mobile browser, it worked and I no longer see really any foreign language posts.

You can double check if it worked by trying to type a post/comment and then hitting the "select language" box. If only your selected languages appear, it worked.

I know at least when I'm posting on kbin instances, undefined isn't really an option -- if you don't set the language, the post won't go through.

On other fediverse instances, there's actually auto-detection of language as an option, followed by auto-translation. I think the lemmy devs are up to their armpits in alligators at the moment, but I wouldn't be surprised if eventually both features come to lemmy once things calm down.

the only thing really necessary would be setting the language to the entire… sublemmy (??) so all the posts there would default to the sub language. I think it’s pretty unusual for a sub to have posts in multiple languages, but at that point the big majority of it would be set.

I don't even have the language selection while posting from Jerboa. But like the others said most people probably won't use it becuase it is annoying to find the language on the slider menu without a search functionality each time. It would be used more if instances and users could select a default language for themselves

It would help if Instances/Communities would set the expected language and you could change it so the default isn't Undetermined.

I don't know if that's possible, I manage neither.