"Please repeat in Vietnamese."
Translation:Làm ơn lặp lại bằng tiếng Việt.
To my knowledge, ở is used to point out a place, a location (where).
ex: ở nhà ga = At the train station.
While bằng is to give precision as to what is used for a purpose, by what mean
Ex: Bạn đi làm bằng gì? = How do you go to work? (literally "You go work by what) Ex: Tôi nói xin lỗi = I say sorry Ex: Tôi nói xin lỗi bằng tiếng Việt = I say sorry in Vietnamese (literally "I say sorry by language Vietnamese)
I hope it helps.