You would have to set your input layout in your OS to iso-de to have native äüö support.
I'll just write down which ansi signals you would need to trigger a ä, ü and ö output if the OS is set to german layout (you cannot trigger a native ä,ü or ö without using german layout in your OS):
ansi= ' triggers a ä output
ansi= [ triggers a ü output
ansi= ; triggers a ö output