Hi, you don't need a California driver license unless you live here. So, you are visiting California , you can drive with korea driver's license. However in California, not many people know that if you come to California, you need an insurance but you can still can drive in California by not having an insurance and you will not receive a citation as long as the car that you are driving has an insurance because an insurance protects the driver and if driver don't have an insurance then the car owner has to have an insurance , that means the car you are driving needs to have an insurance then you will be fine. You don't need an international driver license because it is useless. An international driver license was established during second world at a convention period. Although the AAA still issue an international driver license but you don't need in United States as long as you have a korea driver's license