Most of the time there is no need to translate anything. Flashcards with pictures don't require translations, and the human brain will extract grammar rules and assimilate them via comprehensible input from the textbooks.Interesting....but how do you teach translation/vocabulary to your students if you don't know or aren't allowed to speak their language?
How do you teach what certain words and phrases mean, grammar rules, or, I assume, this part is done only by reading?
You tell them "chicken" or "what's your name?" - don't you have to translate it to them to teach - unless it's something they get from reading material only, where they can see Vietnamese and English side by side.
So, I'd imagine, in a system like that, each lesson would probably have a required reading to get prepared, with a list of words and phrases to learn, with Vietnamese translation.
And how do you help a struggling student who needs something explained or is it not required because it's not one-on-one?
Anyway, most of the time there will be a Vietnamese teaching assistant helping you with any communication/translation issues if they occur.
The TA will do most of the heavy lifting.
The foreign teacher will do all the easy stuff.