"남자가 한국어로 말합니다."
Translation:The man speaks in Korean.
Is the "in" really necessary? Is "The man speaks Korean" an equitable translation that should be accepted?
No, because this sentence ("The man speaks Korean") implies that the man can and able to speak korean, while the correct one(The man speaks in Korean) means that the man is speaking in korean right now, and not in an another language.
I think if you don't out "in" it implies that the man is fluent in Korean. In this situation, he is only speaking Korean in one situation and no information is given on his fluency. Anyway, I made the same mistake.
"The man speaks Korean" implies a knowledge of the language not reliant on his current activity. "The man speaks in Korean" describes his current activity; he is currently speaking in Korean as opposed to a minute ago when he was speaking in English, and later when he'll be speaking in Swahili.
Substitute "multiple languages" for "Korean" and your sentence makes sense (The man speaks multiple languages) but the original sentence wouldn't (The man speaks in multiple languages) unless you were referring to the man acting as a translator or something lol
The man speaks korean can also mean that he van doe it and if he speaks IN korean he speaks that moment in korean
i'm less bothered by whether the "in" is really necessary and more confused about where in this sentence it actually is.
The -가 ending makes it more specific that "the man" speaks. 남자는 would be a little less specific, it could be several men or men in general. It's not the same as in English a/the, but u should check the differences between 은/는 and 이/가.