Translation:Say it again.
It is basically an imperative order, not polite enough.
Some simple changes will do the job :
I translated it as "Say one more time," but DuoLingo marked it as incorrect, the correct translation being "Say IT one more time." Is there a difference?
In English, "say" sounds strange by itself (without and object). "He speaks." is ok, "He says." is weird because you wonder "What does he say?" (It's ok there, because "what" is the object, even though it is far from "say".)
Yes, there is a difference. In English we don't usually say 'say one more time', instead specifying what is said. "Say that again?", "Repeat what you just said', 'Say it one more time"...
"Can you repeat?" is a question. The idea is the same, but the grammar is different.
I had "repeat it, please" and Duo marked it wrong!! BOO! YOU ARE AWFUL DUO!
Well Chinese is a pretty new course, and Duo isn't awful just because it doesn't know that. The more literal translations are more likely to be accepted.
The reason Duo didn't accept it was because it didn't see 'please' inside the sentence, even though a general translation would accept that. I'm not sure if Duo accepts 'repeat it' either.
Chinese is a new lesson. Duo is free and needs the help of users to improve. Report that as your answer, and it will get fixed (though this takes time because there are so many).
To be fair, "repeat it, please" is not a good translation, and should be marked wrong, inasmuch as the 说 clearly indicates to "say" it again, whereas the "it" of "repeat it" could refer to anything: repeat a musical passage, repeat a set of push ups, "wash, rinse, repeat," - anything, really: the sentence does not mean "repeat it, please;" rather, it means "say (it) again."
Yep, it's the English and not the Chinese. If someone wanted to take the Chinese for English course they would need to know some basic English. Just because you don't see 'it' in the Chinese doesn't mean you're not supposed to add it in English. Sometimes you can use your deep feeling for whether a sentence is correct or not - whether it sounds unnatural or not - before submitting.