My impression is that it is just someone who created a community for each language they could think of.

Actually it’s the /r/experienceddevs subreddit mods who created that instance. I had never heard of the subreddit before though but they had a bit above 100k subscribers

Actually you don’t need multiple accounts, you only need one in a specific instance and can interact with other instances (My account is registered at programming.dev).

The UX is extremely wonky and I had to look it up, but you can go to the search in the top right of your instance’s main page (not the “communities” subpage) and search for communities and filter by “Communities” in the top left

The first bullet point in “Project & Toolings Updates” section only has “Changelog #184” without referencing that it’s about rust-analyzer. This should be changed to be more clear