I think it would be great to be able to click a button on a comment\post and have it translate to your language. I think its possible to build a way to include this in a privacy respecting way (im not a coder so forgive my ignorance) if we use something like the google translate scraper that is used for this privacy respecting google translate frontend https://github.com/thedaviddelta/lingva-translate
Making it easier for people to communicate across languages would be pretty sweet for the fediverse.
I would suggest the Mastodon way, choosing the language you are writing your post and additional tabs for different languages or, as additional suggesting, using LibreTranslate instead of relying in propietary services.