Do you have any reason to translate things you are not good at? There are people who are good at both English and Korean out there, why do you have to work on this translation if your translation skill is not even good?
The ones who do the unofficial translations are wdtfs fans, so I think they could tell what is a name and what is a word needed to be translated. Moreover, like Newp said, it was not easy to do this translation work because you choosing a wrong word might result in screwing the whole original sentence up. Which implied that as a translator, even it is unofficial, they do care a lot about their translation's quality. We don't even know if the ones who do the official translation read the manhwa or not though, neither do we know if the author checks their translation or not though.