Cool. How is this related to the Fediverse?

Because URLs are usually in ASCII. That was a standard. Check RFC 1738 and 3986. Now, you can use percent encoding, but why use that. It just complicates things.

You won’t get non latin usernames anytime soon. But you can change the display name using non latin charactets

I use my own self hosted SearXNG.

Is there a good reason why? Even MAL takes user submissions.