(Dot) in domains can be reg'd by anyone anywhere. For .de your Whois admin has to contain a verifiable email account located in Germany. (Dot) us is supposed to be very similar to the .ca restrictions but I believe that the enforcement is poor.
The registrar for .de domains is Denic at www.denic.de
You can register a de domain through a company like GoDaddy and they will assign a "proxy" German administrator. It is easy to buy a .de domain but not so easy to sell one. There is a lot of paper work involved. I owned a few but let them drop because the hassles just weren't worth it. Simply put, all control for your domain is through the "proxy" and you have to go through them for any changes.