Edit2: The solution is working and is enabled now. Reply to this thread if it doesn't work for you.
I've become tired of this stupid issue and therefore decided to solve this at the server side once and for all. It's actually solved now, but first I want you to test my solution, so that I can be sure that no browser has problems with it.
So please, post something here (like äöü) and enter this URL in your address bar before you send your posting:
Firefox 3.5.7, Opera 10.10, Internet Explorer 8, Safari 4.0.4