"The students talk in Korean."
Translation:학생들이 한국어로 이야기합니다.
로 is a very versatile particle that can denote lots of things. In this particular sentence it denotes method.
저는 한국어로 말습니다. I talk in (using the method of) Korean
Have a look at the Tips & Notes, under Speaking a Language in the middle right: https://www.duolingo.com/skill/ko/regular-verbs/tips-and-notes
The correct answer here is "이야기..." yet I was correct according to the app when I picked "대화해요". Can anyone explain?
대화해요 is to converse so I think it's accepted but the proper one is 이야기 since it was in the formal form.
The actual answer wasn't there for me it has the past conjugation of talk instead of the present and it wouldn't accept it but there wasn't anything else there.
At least it was not noted as being wrong without the 도. I believe that here it is again highly contextual