We have a Farsi wikipedia user whose Wikipedia username shows up as '???' - smells like an encoding issue somewhere.
This turned out to be a ridiculous thing rooted in MySQL's inability to do utf-8 correctly. I've updated the database settings, documented them, and added a workaround to the Django settings file. I don't know the user's actual username so I can't fix it, but if you run across this in future and you *do* know the correct username, you can update it through the admin interface.
New accounts going forward should be fine.