If such setting is implemented, please don’t limit it to a single language. Many people knows multiple ones while still wanting to filter out all the other languages they are not familiar with.

That’s not a compatibility table, that’s a comparison table (literally from the table itself). I’m not looking for what Firefish can do and Mastodon can not, I’m looking for how are those features interpreted in Mastodon. I’m concerned about discoverability and access. Right now Mastodon has way more users than Firefish and I wouldn’t like to post things only to end up being visible only by people with Firefish accounts.