They were actually talking about it during yesterday's game. Although he's not fully fluent, Kim has a very good understanding of English. He generally understands everything that is said to him and is able to communicate back pretty proficiently. In fact, the Boston announcers said they had been in the bus going to a game with him recently, and they couldn't shut the little chatterbox up.
I would assume that he uses an interpreter just so that his points come across properly, and he doesn't have one of his statements misundertood. Can never be too careful around the press!!
"One of the teams represents truth, justice, the American way, and underdogs everywhere. The other represents George Steinbrenner!" - U.S. News and World Reports columnist John Leo on the difference between the Mets and the Yankees.