[korisnik]

>North Korean and South Korean are completely different dialects

>I can't see a dictionary like that being of any use to his family.

I assume you don't speak any Korean and are talking out of your ass.

The standard Korean used in South Korea and North Korea are both based on the same dialect - Seoul dialect. There's vocabulary differences, but nothing that would prevent a (South) Korean-English dictionary from being useful to a North Korean person.