Comment 1 for bug 1828923

This is a restriction of Django in combination python2:

"... Unicode characters have always been accepted when using Python 3. Django 1.10 officially added Unicode support in usernames, keeping the ASCII-only behavior on Python 2."

See: https://docs.djangoproject.com/en/1.11/ref/contrib/auth/#django.contrib.auth.models.User.username

So the switch to python 3 will accept a wide range of additional characters. Tested 'ß' in usernames, also polish characters in the python3 branch.

But we need to change the database encoding to fully support unicode (e.g. chinese characters), which means the length of text columns shrinks and thus there is a possibility to loose some of text in old entries. So this has to be done carefully.