@riley @BeAware it will depend on what translation software the instance uses and whether they want to feed even more content to AI.
Just checking off what language you use means it's easier for everyone.
Using language settings on posts means that people not interested in posts in other languages can filter them off as well, instead of having them shown up in the time line.
It's just being generally nice and polite to other users, which is (I thought) one of the main rules.