"Degene die de auto verkoopt vraagt een onredelijke prijs ervoor."
Translation:The one who is selling the car is asking an unreasonable price for it.
What is wrong with ...he who sells the car is asking an unreasonable price...?
Actually, degene can mean he or she, and it's perfectly good English to say "He who..." or "She who..." (although a bit archaic) for "Degene die..."
Het volgende gekopieerd uit de Van Dale: Betekenis 'degene'
Je hebt gezocht op het woord: degene. degene 1(enkelvoud) he, she, (meervoud) those: degene die … he who, she who.
I agree that to use "he/she who..." is archaic and therefore would suggest it isn't perfectly good modern english. I think it confuses learners if archaic translations are used, even if they happen to be technically correct.
I actually often use this phrase in English more than the said phrase abovementioned.
I like having it as an option, at least, because it helps me understand the Dutch construction better. I can "translate" archaic English constructions and words into modern usage, but I'm not trying to learn English, anyway. If I know that "degene die ..." means "he who ..." then I understand what "degene die ..." means and how to use it. And learning how to use Dutch words and constructions is why I'm here. (See also herewith, thereon, whereafter, etc.)