Ok, so wasn't (partly) the point of Lost in Translation the fact that some things might not, well, be understood? That language can still be a private exchange that is necessarily lost on a wider public? That we cannot have access to all exchanges, all speakings-across-spaces, at all times? That in the midst of a wider space of shared language you can still have your own private conversation and generate meaning that an eavesdropping audience doesn't/shouldn't have access to?
Well, some creative youtuber with way too much time on his hands has supposedly figured out what Bill Murray's character says to Scarlett Johansson's character in the film. Wikipedia says one thing (second to last bullet point in the Trivia section); this youtube video claims another. You decide. Me, I preferred not knowing -- and as far as I'm concerned, I still don't really know. But well, here you go: have a look and have a perfectly lovely scene in an otherwise meh movie get completely spoiled for you. You are forewarned.