JIN: (Resurfacing after another attempt at freeing Sun) Ahh...Uhhh
SUN: Jin. You have to go.
JIN: No. I can do this.
SUN: No. No, you can't. (crying) Please go.
JIN: (lovingly cupping Sun's face) I won't leave you. (Jin goes under attempting to free Sun as the water has now risen to neck level)
JIN: I'm gonna get you out of here.
SUN: (holds Jin's face imploringly) Go... Please! Go.
JIN: (helplessly looking around) 당신하고 같이 있을게. 다시는 떠나지 않을거야. (Subtitle: I won't leave you. I will never leave you again...) [in English] I love you, Sun. (they embrace and kiss)
SUN: (crying) I love you. (They embrace and kiss as water rises to their faces - the sub falls to the bottom of the ocean - completely immersed - the lifeless hands of Jin and Sun separate - Sun's body floats, her hair covering her face.)
This is one Lost's most heart-wrenching/beautiful scenes. Even collecting the images to use for this post had me tearing up. It left a big impression on me that's just as strong today as the first time I watched in horror as two of my favourite characters passed away in the most tragic of circumstances.
For this reason, I found it (to put it mildly) bemusing to hear that for some, the scene was a failure because of - get this - the language that was used. The people that had the issue believed that the whole thing should have been in Korean. While I understood why this would have been acceptable, I can not fathom how such an extraordinary scene could be 'ruined' (a very strong word) because of this.
I was accused by some of 'defending the indefensible' because of my dedication to Lost. The truth is my love for the show is the reason I am highly critical of it at times (note my thoughts on Stranger in a Strange Land and especially the character of Achara for which I will never forgive the writers for).
I clearly outlined the reasons why I thought they were right to script the scene (mostly) in English. Ultimately, I came to the conclusion that the producers were 100% correct to do it the way they did.
Those words (in the sub scene) to me had FAR more impact in English than they would have in any other language I do not speak. It's as simple as that. Do I understand that some people would see it differently? Yes of course. Do I think that in real life they would have spoken Korean? Quite possibly. Equally they could have said it all in English as well as that was the language they'd been speaking with the other Lostie's just seconds before. Lost is entirely fiction where sometimes, decisions like this come about because of lengthy discussions between writers and producers. I guarantee there would have been a heated debate about this in the writers room.Across The Sea" that signified the change from Latin to English (even though they weren't speaking English at all), similarly we could view this scene in exactly the same way.
There is a scene in Season 1 where Sun and Jin are in the caves and having a fight in Korean (shortly after he discovers she's bilingual and long before Jin learned any English). Sun, crying, instantly moves from speaking Korean to English saying "I was going to leave you, I was going to run away". Jin looks at her and till this day, we're not sure if this was a case of where the writers chose to switch to English for emotional impact (where really it was said in the characters native tongue), or whether she really did say those words in English in the context of the 'Lost universe'.
The "language-switch" technique on Lost was quite common. In the France flash-back episode with Sayid (where he gets taken prisoner by the husband of the woman he previously tortured), the scenes between the two men begin in Farsi and then at a pivotal moment switches to English which continues right through till the end. Viewers know they weren't speaking English at all, but the switch makes the 42 minutes of dialogue much easier to follow as there is no need for subtitles the whole time. Flash back scenes with Sayid in Iraq often did the exact same thing. They'd start in Farsi and then switch to English.
I believe that the issue of language in the sub-death scene is almost a moot point because we’re free to believe whatever we want. Personally, I do not care which language they actually spoke. What matters to me is the emotional resonance that I feel was enhanced considerably by the producers choice to script the majority of the scene in English - a choice that is equally plausible had it have happened in real life.