There is a plugin called "german permalinks" out there:
ATM, when I use for example "ä" in the title, it is turned into "a" in the URI, however the correct form would be "ae". The above plugin corrects exactly this and does not disturb non-german blogs, as it only replaces the german characters. Maybe someone could check and - if possible - implement it.
BTW: Thanks for the great service here, it is VERY appreciated!