There is an option under settings>filters>looking for language filters, but adding a language does not work. Is there a way to filter out posts in languages I don’t speak?

It probably doesn't work because those posts weren't tagged correctly. The language tag should have been mandatory on Lemmy from the beginning. Now most posts are tagged either Unknown or English.

I haven't seen it on the app but it's in your account or profile settings if you use the web. I know it's there because a few days ago I accidentally deselected English and I wasn't able to see my own posts.

I could have been more clear with my question. The option is there in the app but it does not actually let you add or remove languages. But yes, even if you could select language options, if posts aren’t tagged correctly it won’t work