"The day after tomorrow, they will have a discussion about Dutch culture."
Translation:Vào ngày mốt, họ sẽ thảo luận về văn hoá Hà Lan.
I don't know if you are trying to add to what he said or to say that he is wrong but if it's the latter then he said "NGÀY kia" not "HÔM kia". Either way I have no idea who is right or wrong.
I'm sorry, it was a comment over 7 month ago. I've never used "ngày kia" as the day after tomorrow, and it was my first time coming across it as well. instead I've always said "hôm kia" and "ngày mốt", respectively the day before yesterday and the day after tomorrow.
that being said, I've asked my parents since then. my dad, who is a northern native speaker, was rather surprised when hearing about it. to be fair, he moved to the South in 1954, and we live abroad for over 35 yrs. my mom, who is a central native speaker, knows "ngày kia" being the day after tomorrow but I don't recall ever hear her say so. they both always use "ngày mốt".