First i was surprised, that your website accepted special characters,
but than i realized, that i can't properly log into this account.
I know from another website, that the letter "ü" sometimes gets converted into: "├╝"<- (i'll bet, no one has this in a brute-force list, which is the main reason why im using this ^.^)
But this wasn't the case here.
Can you change the corrupted letter (or whatever it is) in a "ü" (or insert this value into the SQL table for my username):
"Füchschen". The email should be the same as used in this forum. This way you can find it.
Or at least whipe my account, so that i can create a new username
Ether way, i suggest you put a warning upon registration, if characters can't be used on your website, like the way
this forum works here. Here i wasn't able to use "Füchschen" as a username.
Hope this helps you for improving this website and i also hope you can help me as well.