Re: Sun/Jin Subtitles
The rule is... NO subtitles if there's a non-Korean speaking actor in the scene with them. That way, we, the audience, experience the moment exactly as Michael did (in this case). I'm sure Michael wanted to know what Jin was saying, too.
We only use subtitles when the scenes are privileged between Jin and Sun. And that goes for any Foreign-speaking character in flashbacks as well.
Sorry if that frustrated you. But luckily there are plenty of sites ready to tell you what Jin said.