Solution found: Xnest with German Keyboard / Umlaute
I wondered why I missed German Keyboard mapping when I started Xnest
inspite of my whole Linux is running with German Language fine.
After checking every possibility I finally found the solution by trying.
As I searched the whole web without finding a solution but found many posts of
people having the same problem I want to post the solution here.
It is the -kb option!
Xnest -query IP_or_Hostname :1 -kb
Xnest -help says:
-kb disable the X Keyboard Extension
Hope this is of help for someone.