It was "old beast lunatic" in Korean, "dotard" was an approximate translation.
North Korea has always thrown out hilariously undiplomatic insults to foregin diplomats and world leaders - look at some of their comments on Hillary Clinton, for example. This is the first time they've had the opportunity to use them on a leader as thin-skinned as Trump though. No-one else dignifies their baiting with a response, instead farming out a comment to some low-level functionary.
Every time they provoke Trump, he visibly flinches and responds with some dipshit chest-beating on Twitter. North Korea then responds with another missile or nuclear warhead test. You don't need to be a genius to see what their game is. You do have to wonder what sort of idiot keeps walking into the same trap, time and time again though....probably some old beast lunatic of some kind.
