FEATURE: make username suggester suggest `user1`, `user2` etc. for input that contains invalid characters only (PR #14179)

We were suggesting 111, 1111, 1112 before.

See the discussion on Meta.


It might be nice to localise this? (and therefore, allow admins to customize it via the translation editing UI)

Oh, right, will add localization.

I’ve pushed localization support.

There might be a problem with the fallback username for non-English locales if the translation contains Unicode characters which aren’t allowed (allowed_unicode_username_characters) or if unicode_usernames is disabled. It might be a good idea to use the English translation in such a case.

Looks like we have a similar problem with the anon usernames.