The show just had them sounding like jibberish to show what it is like for Jin.
That's why they never have sbutitles if Jin is speaking to an English
speaking character - we just have to figure it out by his gestures or maybe
catching someone's name.
When Jin is talking to Sun he says "I can't talk to anyone." He has picked up
a few words, but he can't have conversations yet and he wants to.

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Have a cluckety cluck cluck day.