The main language spoken on Jeju Island is Korean. However, it is the Jeju dialect of Korean. Just like how some people in the United States talk differently depending on where you live, people speak differently throughout South Korea, too. Examples in English are soda vs. pop, water fountain vs. bubbler and other things like that!
The South Korean won is used on Jeju Island and everywhere else in South Korea. Every one U.S. dollar is equal to around 1,100 Korean won. When you see the price of something in South Korea, you will see this symbol in front of the price: ₩, instead of the U.S. dollar sign, $.
A normal-sized 12 ounce bottle of water in Souh Korea costs around ₩550, which is around $0.45.
The best meal that I had this week was dak-galbi (proncouned da-kal-bi). Dak-galbi is a large stir-fried dish that you normally only eat at a restaurant. This is because it is cooked on a special very large plate in the middle of a table. The waiter puts diced chicken, sweet potatoes, cabbage, rice cake, garlic, onions and spicy sauce on the large hot plate. Everyone sitting at the tables digs in after a few minutes once everything is cooked.