How to restart Gnome 3 without logging out
Press ALT+F2 and enter "r" as the command.
If you got an american keyboard layout after this you can change it back by using
setxkbmap de
with the appropriate country code.
You can also use the dconf tool to set desktop/ibus/general/engines-order and use-system-keyboard-layout to your preferred layout and to true to use you system settings.