English in Busan is not commonly understood. The use of English by foreigners is commonly resented by Koreans. Yet it is universally taught in schools, so if you are patient, young people should know enough to help you out. Taxi drivers will be unlikely to have much English knowledge, and the pronunciation of Korean words can be difficult, so it's advisable pick up a tourist map from your hotel or a train station to point to where you want to go. If you don't have a map, write down the place you want to go. Note that there is a translation service the taxi driver can call up if needed. Because most foreign tourists to Busan are from Japan, some level of Japanese is often understood by people working in hotels, restaurants, taxis and other tourist focused services, so if you know a little Japanese, you might try that, if English fails. However, Japanese language is a historical reminder of Japanese colonization in the past and its use can be resented by locals.