Koreanic languages
Koreanic is a small language family consisting of the Korean and Jeju languages. The latter is often described as a dialect of Korean, but is distinct enough to be considered a separate language. Alexander Vovin suggests that the Yukjin dialect of the far northeast should be similarly distinguished. Korean has been richly documented since the introduction of the Hangul alphabet in the 15th century. Earlier renditions of Korean using Chinese characters are much more difficult to interpret.
https://en.wikipedia.org/wiki/Koreanic_languages