Unicode characters in Django usernames
It is really not a problem - because this character restriction is in UserCreationForm (or RegistrationForm in django-registration) only as I remember, and you can easily make your own since field in database is just normal TextField.
But those restriction is there not without a reason. One of the possible problems I can think of now is creating links - usernames are often used for that and it may cause a problem. There is also bigger possibility of fake accounts with usernames looking the same but being in fact different characters, etc.
I am developing a website using Django 1.4 and I use django-registration for the signup process. It turns out that Unicode characters are not allowed as usernames, whenever a user enters e.g. a Chinese character as part of username the registration fails with:

This value may contain only letters, numbers and @/./+/-/_ characters.

Is it possible to change it so Unicode characters are allowed in usernames? If yes, how can I do it? Also, can it cause any problem?