I'm no expert, but I use a British keyboard on my RPi, so I have encountered the need to change the key map.

I would expect that the 'de' key map file will be designed for this keyboard layout: https://en.wikipedia.org/wiki/QWERTZ#Austria_and_Germany
Perhaps check whether your keyboard looks like that one, and has the '<>|' key between the left SHIFT key and the 'Y' key. If it doesn't, then I think you will need a different key map file.

If the keyboard looks right, but the key either does nothing or produces the wrong characters, you could try attaching it to a different computer both to see if that key works there, and also to find out what keyboard language settings it works with there.