Here’s a list of communities related to conlanging (the art of creating languages) and conworlding (worldbuilding for its own sake rather than for a book or game.) These communities are fairly quiet, since these hobbies are quite niche, but I thought I’d put this out there.
I assumed they were aware of each other and simply differed in moderation style or the type of user they wanted to attract.
I have, however, been toying with establishing a presence in the fediverse for conlangers/conworlders to congregate; likely not Lemmy, but NodeBB, as I like the more permanent nature of forums compared to more modern social media. As for non-federated conlanging communities, there’s the CBB where I hang out most, the unrelated ZBB, both running phpBB. But the granddaddy of conlangery on the internet is probably the conlang mailing list.
I can only vouch for the CBB, as I’ve merely lurked briefly on the ZBB and have never checked out the mailing list, though it’s on my todo list.