[KS] Languages spoken in Korea throughout history?

[Bert Edens]

Greetings, all...
	Are there any documents that summarize which languages have been spoken in 
Korea throughout history, especially pre-Three Kingdoms? Obviously, this 
century and back to King Sejong and before aren't too hard... But what 
about pre-Three Kingdoms? How far back can we go and know what language(s) 
were spoken?
	Thanks for everyone's time.

- Bert Edens