This does not work in German because fighter (Kämpfer) is gendered as male. There's is female version of it though (Kämpferin). We have Feuerwehrmann and Feuerwehrfrau. Correct gendering in German is (I say that as an older a male) a bit complicated and makes the sentences usually mich longer or sound weird.

There was a joke solution to this that I really liked: add a "y" to the end or all gendered words: Feuerwehry, Frisöry, Mitarbeity, Erziehery, Arzty etc.

Monster or Ungeheuer would work too. Feuerwehrmonster.

In frontend development, it's pretty common to use German to stress test UIs, as it's a commonly used language with a lot of long words. It reveals all sorts of UI issues - text that doesn't wrap properly, buttons that are pushed off the screen, etc.

I don't know German, but I do like the idea of using compound nouns rather than inventing new words.

It's also common to test UIs with Arabic, to test handling of right-to-left languages. At work we have a "fake RTL" language that's English but rendered RTL. It's interesting because everything is flipped - for example, a left-hand sidebar is instead on the right side in RTL languages. Company logo is at top right instead of top left.