That’s a nice example where English fully compounds the word while German and Dutch, languages where compounding is more usual, use a hyphen (“Orang-oetan”, respectively “Orang-Utan”).

Looking at the various translations on Wikipedia (https://de.wikipedia.org/wiki/Orang-Utans#/languages), that could be because they took the word from different languages. For example, Bahasa Indonesia has “Orang Utan”, Bahasa Banjar “Uranghutan”