In The Confidance Man episode we see a scene where Jin comes upon Sun & Michael as he is giving her the eucalyptus. They are speaking English but seem to stop moments before Jin can hear. Jin then blasts Sun in Korean & we don't know what he is saying since there are no subtitles. Why not? I feel it was important to know if he actually heard her or not & judging from the translation of what he said, he does NOT know.

Why no 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.