While I do not have first hand experience, my therefore unqualified guess would be that the firmware installed ought to be the Korean one. Even if the firmware is Korean, there should be the option of choosing English language. If it is set to Korean it is "only" a matter of navigating to right place and change from Korean to English.
I have got a Kenwood DAP bought here in Japan where I live during this year. It was used and (of course) set to Japanese. I am in the early intermediate stages of studying Japanese, so where I could not understand what it said (a lot of places), I could at least guess and find the correct menu and change the language.
Anyone with first hand experience might want to chip in?