Facebook does not accept website domains with german umlauts ä,ö,ü - Solution: Convert them to Punicode

I tried to add a Website URL to my facebook page which contains german Umlauts ä,ö,ü. Facebook kept telling me, that the URL is not valid.

How-I-fixed-it:
Convert the Domain URL into Punicode, using tools like:
http://tools.macx.de/tools/idnconvert.html

This makes it look like:
www.xn--neuenbrger-adventsfenster-kwc.de

The funny fact is, after entering this as website URL in Facebook, it's automatically converted back to the original form including the Umlauts :-)