I have been searching for a while and haven't been able to find an answer.
I found that wordpress doesn't allow non-English character in username (and no longer give a descriptive error message from some previous version), and I know that I can use whatever characters in the nickname.
The problem is I'm trying to write a plugin that integrates wordpress and another forum where non-English characters are allowed in usernames.
So, is it alright to manipulate the filter on the login (register) page?
Or do we have the restriction there for something else other than just security issues?