오 ~ 한국말 좀 늘었네
And what does "~" mean?
~ is just a filler to make the message feel more casual/positive, similar to a smiley.
Korean = 한국말
좀 = 조금 = a little
늘다 = improve (늘었다 improved)
-네 to be surprised about the fact.
오 ~ 한국말 좀 늘었네
Oh your Korean has improved a little! ~