Well, the title already states it:
I'd like to know, which characters are never allowed inside a username (not ingame, but the account-name) or alternatively: which ones are allowed?

I know there are some invalid ones like # or %, but there are also some legal special characters like Æ ... so ... I'd like to have a list

Allowed: !()_-=.@[]{} and Alphanumeric
Space is also valid

I dont think i forgot anything else.

And it looks like these are also supported:

éíáýúóå