Koreans all speak and write the same language, which has been a key factor in their strong national identity. The Korean language, like Hungarian, Mongolian, and Finnish, is classified as a Ural-Altaic language. 한글 (Hangul), the Korean alphabet, is composed of 10 vowels and 14 consonants. A group of scholars, under the patronage of King Sejong, invented Hangul in 1443. If you have more interest in the Korean language, you could learn it at the site of Let's Learn Korean. In July of 2000, the New Romanization System for the Korean language has replaced the old system proclaimed in 1984. According to the new system, many names of cities and provinces will be changed in Romanization. However, since all maps and road signs cannot be changed at once, you can still see the old romanization system. Thus, when you locate a certain city, you could be confused. Busan will be used instead of Pusan in romanizing 부산. Kyonggi-do and Gyonggi-do are the names for the same province. So, as long as pronunciation is similar, please consider they're different romanization for the same place in many cases with some exceptions.
Since English is a required course from the 3rd grade at the elementary school in Korea, many Koreans, especially those educated and younger generation, can also speak some English, with the limited proficiency, though.