Hi Stig...
As I too was interested to know how the coding on gliders worked, I took the liberty to reproduce your question over on the LEMB. With thanks to Ed North, he pointed us towards the excellent LuftArchiv site here:
http://www.luftarchiv.de
Locate and click on the Luftfhartindustrie link on the left hand side of the homepage. Under the sub-heading Segelflugzeuge, click on the 1922-1945 link which will enable access to a detailed explanation on the coding system employed.
Cheers
Peter D Evans
LEMB Administrator