The auction description says that it is a XT keyboard.

There are similar keyboards that talk AT, i.e. same as PS/2.
There is already a known keyboard of that type with German layout called the G80-0530. They were apparently made before Cherry decided to write the layout variant as letters instead of digits.
Previously seen keyboards have PCB-mounted Cherry MX-switches with diodes for NKRO.
See
http://deskthority.net/wiki/Cherry_G80-0499 .
If you want to use the keyboard as is, I would suggest that you put a Teensy in there with Soarer's XT-to-USB converter loaded. You should keep NKRO.
The keyboard is really wide, though..