I see that one cant create a Hebrew username, i understand that at some sites this would be confusing, but is there anyway if the site is only for Hebrew speakers, is there any problem to allow it?
Coming form phpBB where Hebrew usernames are allowed…
Its a very complicated change to allow this, touches lots of places. Username rules are hardcoded in at least 3 spots.
Nearly the same username rules as twitter, except we now allow up to 20 chars.
If you want full Unicode names to show, enable that preference.
I hear yea,
By name you mean display name right? Not username…
Coming from phpBB platform, this might be a bit of a problem.
It is an important change…
I’d like to see full unicode usernames. However note that doing this correctly is tricky and can have security implications. One needs to take care with canonicalization (same character, encoded different ways) and there is potential for user confusion (different characters, but look the same).
I.e. “Α” looks very similar to “A” but is not the same from a machine point of view (one is LATIN CAPITAL LETTER A and the other GREEK CAPITAL LETTER ALPHA). Are you talking to Adam or Αdam? Are you sure? 
Yes it is terribly complicated, especially given the URL structures here. Its so complicated that companies like Twitter totally avoid solving this.
Not saying its an impossible change, just a very expensive change that will also take up a bunch of ongoing cost.
yes, I’m from china, we have a lot of Chinese username from old forums. I just want this feature baddly.