Translation:The rooms in this hotel are not very clean.
The Chinese sentence means all the rooms in that hotel, not just one room. So the original translation is correct. Your translation is not the same as what it means.
It's not an obligatory plural so singular translation should be accepted. There would not be a different sentence if there were only one room in the hotel. If one wanted to make it clear that there are multiple rooms, however, they could write 都是不太干净的
Please help educate us by showing us which Chinese sentence would have that meaning.
這間酒店的房間不太乾淨 Most of rooms
這間酒店有幾間房間不太乾淨 Several rooms
這間酒店有一間房間不太乾淨 Only one room
不太乾淨 has too meanings, one is not clean, the other is haunted.
There is no way of ascertaining plurality here! "The room in this hotel is not very clean" should be accepted, no?
I think the reason it should be plural is because of the measure word "家“, which emphasizes that this is the entire building (and all of the rooms it contains). If it was just a "hotel room" (with the "hotel" only serving as an adjective instead of taking the possessive role), the sentence would be something like ”这个酒店房间不太干净。" Thus, if a Chinese person hears this sentence, they will always think the sentence is in the plural and never the singular (as I have tested on many willing subjects).
My answer was "This hotel's room is not very clean" (wrong) I wonder if "This hotel's rooms are not very clean" would have been accepted.