ConTeXt has various language codes, listed in this article at the ConTeXt wiki. I do not see Korean listed. I have tried \language[ko], and the document compiles, but I have no way to verify if it is successful, as \language[anything] also compiles.
(Just copying Taco's response to an answer to get this question out of the list of questions without answer.)
To specify Korean text, use
\language[kr]
Taco also mentions [...conversion=kr...], but I don't know what that means. Grepping the sources for conversion= suggests this key is used with commands like \setuppagenumbering and \setupsubformulas, but mostly with the value conversion=romannumerals. I personally couldn't get conversion=kr to work.
