Aviation regulator in Germany?

[FL310]

Rajam, there is nothing like a radar endorsement in Germany. What you can achieve is a simple validation of your ICAO PPL-A which will entitle you to fly single engine aeroplanes (land) with a MTOW of 2,000 kgs under VFR...nothing else.
Also all controlled aerodromes operate on English language, this beside the German one of course, be aware that most airfields still operate only in German language as they are not certified to use the English language, the reason is to have certified radio operators available at all times in both language. Also this appears odd, in Germany there still exists an all German Radio Certificate valid to operate on German registered aeroplanes under VFR procedures.

To get something directly from the licensing department, use following phone numbers:

Head of department
Mr. Kramer [phone]
Officers
Mrs. Kluth [phone]
Mrs. Salle [phone]
Mr. Wadsack [phone]
Mrs. Greve [phone]
Facsimile [phone]

There is of course a complete answer to your questions in the AIP, you may have friends in Germany who need to scan and mail the respective pages to you.