There is no list of approved translators for Korea. In Seoul you should just go to a notary public or lawyer's office. They usually have a translator on staff or nearby that they use. The translator will translate the document and then swear an affidavit, which the lawyer will notarize, attesting to the accuracy of the translation.
BTW, if you need help regarding a Korean application, join this thread.
http://www.canadavisa.com/canada-immigration-discussion-board/sponsoring-my-korean-wife-for-permanent-residency-t137874.0.html