Scientific themed communities. Excellent.
Really love Mander
😘
star trek.website
You can find a list here: https://lemmy.world/post/1886401
Linked in a comment within that post, this appears to be an extremely comprehensive list:
https://kbin.social/m/specialized_instances/t/186667/Big-list-of-specialized-instances
waveform.social
there’s a couple of furry ones, yiffit.net (NSFW) and pawb.social (idk if they allow nsfw or not)
I’m not sure if there’s any language exchange or language learning focused instance.
Probably it could also work if each regional instance had a focused language learning community.I know about https://programming.dev and https://mtgzone.com I wish there were one about gaming and another about fanfiction