I can't help with the German, except to recognize that slang terms are very localized. My family name means 'wagontongue' and has come to refer to the handle of a golf cart or luggage carrier --- but in Austria it apparently is a common term for ... the Devil! I can't figure out the connection, but slang is rarely logical.

I did have an experience with the French equivalent mentioned above. When I first visited Paris as a recent graduate, I linked up with a couple of classmates who were studying there and living with a French family. I had never studied French but had some background in Latin, and was faking my way with a good ear for French pronunciation and the hope that cognates would carry me through and it worked pretty well.

I was invited to dinner with my friends' host family who spoke little or no English, and I ventured to explain my linguistic technique by describing my ... habit ... of using cognates.

"J'ai l'habite," I started and my friends immediately chimed in in chorus to drown me out, "L'habitude!" They whisked me out to explained that I had just said that I had a dick! I guess I was embarrassed enough to remember it although it was back in 1949.