Well, after reading your previous post I looked it up and there is literally a book called "Der Untermensch" and that's described as "how the Nazis described the Jews, Slavs and Roma" (all of which were persecuted by them).

I am not fluent in German and didn't live in Germany long enough to pick up that kind of subtle language rules, so wasn't aware that it sounds really wierd in German. It would also sound really wierd in my own motherthougue, Portuguese, and we would be using the equivalents of the words you used in German, though using the singular form is gramatically valid and definitelly carries an old-fashioned racist tone.

I suspect that using that form (at least as a book title) was most definitelly purposeful and for maximum distancing from the target group, a bit like an 18th century racist might title a book "The African".