I've got it running with satisfactory results with the mapping
The "de.map" must be out of stone age computing and can't imagine who is still using this antique keyboard! It does not support the modern umlaut keys.
What is still missing is the Euro symbol. I tried "loadkeys euro1.map" but - not knowing whether it works - there is a remaining problem with the font. So stepping into another question: "How to load a iso-8859-15 compatible font?"
Well, many thanks so far. I believe I can live without the Euro symbol in the console modus for a while.
Btw, can you say what those mappings in "querty" are good for?