As a German, I might not have thought of that but would absolutely use it to translate Verschlimmbesserung. Does it sound "normal" enough to native English speakers?
It's totally plausible portmanteau. I get the feeling thought that it sounds more marked in English than in German where these kind of mashups are formed more freely.
It's definitely a normal-sounding, memorable word for us native English speakers.
Meanwhile I won't be able to remember that German word longer than it takes me to close this tab. Vershumthingsomething.
Thumbs up, let's settle on that translation
I'm Dutch, sounds pretty good to me
The sibling post's "disimprovement" sounds more natural and has parallel form with pre-existing broadly accepted English words like "disincentive" and "disinfect".