"Who is the fisherman?"
Translation:Ai là ngư dân?
To translate a question from English into Vietnamese, the easiest way is to translate it word-by-word.
What = Cái gì (a non-living thing)/ Con gì (a living thing). Which = Cái nào/ con nào. Who and Whom = Ai. Why = Tại sao. How = Làm sao. When = Khi nào.
Your sentence is also correct and by far is more common in use. All interrogatives above can stand at the end of a question and make a slightly different meaning in terms of the point of departure of the message, but I think the grammatical point should be given in other lessons. Too many transformations of sentence structures would put the learners in difficulty.
I agree, if you mean that his answer should be the standard answer or at least accepted. I put down the same thing because his construction seems to be is the more common word order for a Vietnamese question.
Intuition tells me that "Who is a fisherman?" should be better in this case. "the fisherman" is not wrong, but it suggests that the interlocutors know about it, which in fact is not in this case.
Interesting...what is it about the sentence that makes you think that? Wouldn't "Ai la mot ngu dan?" = "Who is a fisherman?"
In English, "the" is a definite article. An entity modified by 'the' is either in the discourse, or in our general knowledge of the world that identifies it for us.
In Vietnamese, the equivalence to 'the' is the post noun complements "đó", "đấy", "này", "nọ" (as in "cái đó", "cái đấy", "cái này", "cái nọ" = "the thing"). Note that, the post complements encompass the grammatical use of both the article 'the' and determiners 'this', 'that', 'these', 'those' and sometimes the pronoun 'it'. We also don't use any post complements to call an entity of general knowledge or an entity that is one of a kind for the first time it happens in the discourse, for instances: The Eiffel Tower = Tháp Ép-phen, the USA = nước Mỹ, the President = Tổng thống, etc. To refer to the entity again, we sometimes use post complements, but they are optional.
To sum up, in my opinion, the translation of 'Who is the fisherman?' into Vietnamese is: "Ai là ngư dân đó/ đấy/ này/ nọ" because it suggests that the speaker and the listener have known about the specific entity before the sentence takes place.
Your translation of 'Who is a fisherman?' is correct in accordance with the rules of thumb in translation. But normally, the Vietnamese omit "một" and go with "Ai là ngư dân?"