I found this entry
Section "InputDevice" Identifier "Generic Keyboard" Driver "kbd" Option "CoreKeyboard" Option "XkbRules" "xorg" Option "XkbModel" "pc105" Option "XkbLayout" "us" EndSection
in my /etc/X11/xorg.conf and changed "XkbLayout" "us" to "XkbLayout" "de". Now it works perfektly.
I found this entry
Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "CoreKeyboard"
Option "XkbRules" "xorg"
Option "XkbModel" "pc105"
Option "XkbLayout" "us"
EndSection
in my /etc/X11/xorg.conf and changed "XkbLayout" "us" to "XkbLayout" "de". Now it works perfektly.