Hi Sebastian Wiehl,
Thank you for your interest in Sitefinity and for getting in touch with us.
Thus far, we have not worked on such functionality, because the URLs support only ASCII symbols. We do not have a workaround either because most of the languages are using UNICODE and this option would be usable only for a narrow range of languages.
We will include this feature in our ToDo list and consider it for one of the forthcoming releases.
the Telerik team