Hello Jörg ,
Thank you for using our services.
Some of the reasons that we are allowing special characters in the URLs is that we want to be able to provide localizable urls, as well as the fact that we have had numerous requests to allow for special characters in the URLs. Right now you can change the generated url while you crate the page, however I am going to log such a feature request - to be able to provide rules on url generration.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items