Ok but hear me out. Thorin snaps out of goldsickness a little earlier, just in time for the elven army to show up, so the dwarves and Thranduil and Bard all meet to negotiate together.
Thranduil, upon walking into the tent and seeing Bard for the first time: decides the best thing to do in this situation is to give a rather detailed and explicit description of all the things he wants Bard to do with him, in Sindarin.
Thorin, who does not speak Sindarin but sees Bard's eyebrows fly up and really doesn't want him any more angry than he is over Thorin setting a dragon on his people and then nearly going back on his word to help them: If he wanted to insult you, he'd do it in Westron. Trust me on this, I would know. It was probably something nice.
Bilbo, who does in fact speak Sindarin, grinning next to Thorin: Oh, it was VERY complimentary.
Thorin, desperate to not cause a diplomatic incident: You know what he said?
Bilbo: Oh I'd be quite happy to translate.
Thranduil, who was entirely unaware that anyone else here spoke Sindarin and is trying to cover his embarrassment: Absolutely not.
Bilbo, having the time of his life: Oh don't be so upset about it, we hobbits aren't nearly as prudish as the rest of you.
Thranduil, getting defensive: That was not meant for your ears.
Bilbo: Well if they were meant for his I would suggest saying them in a language he can understand.
Bard, who spent years working with elves, somewhat amused and in pretty decent Sindarin: Oh I understood.