Why the correct translation is not "Who are fighting there"? I think the interrogative pronoun "ki" and the verb "harcol" are in plural.
They are plural in the Hungarian.
But in English, we use singular verbs with "who" most of the time.
I agree with mizinamo on this one. Even if the hungarian sentence uses kik harcolnak the best translation is who is fighting, because English generally prefers the singular is even in cases where it's obvious who refers to a plural. who are just sounds strange, unless it is clear from the sentence (or neighboring sentences) grammatically (not implicitly) that who is a plural: who are those people fighting there?
If you literally translate this sentence, the correct translation is: Ki harcol ott? Egy katona. A soldier. In Hungarian we use singular or plural verbs, depending on the subject/s.
Because the English grammar is not correct.
We do not use “do” when asking after the subject.