Hi,
you can add a second keyboard-layout for German and then switch between the two:
Configure Your Desktop (KDE control center) -> Personal -> Regional & Language -> Keyboard Layout (or from a terminal and in KDE4: kcmshell4 keyboard_layout)
then on the right panel select
Enable keyboard layouts and from the list below that add the German keyboard to the Active layouts, then click
Apply and you should then see a flag sign for the keyboard layout in the panel at the bottom right of your desktop. Click that flag to switch between the keyboard layouts. To find out which key matches which letter on a German keyboard check
here.
good luck,
-p.