is it safe to remove language files to save space in osx?
Just to provide an actual answer to this, even if it is speculative...

Like some of the commenters, I've also tried this in the past, with varying results. I don't remember specifically which apps were affected, but it was sufficient that I needed to reinstall some.

I'd say on balance it's simply not worth the risk/effort, balanced against the amount of space they take up on your drive.

I will also add that a lot of those clean-up apps like to invent 'problems' that they can 'solve' for you, in order to justify their existence.