"They discuss the book about Korea's economy."
Translation:그들은 한국의 경제에 대한 책에 대해 대화해요.
can someone explain the structure of this sentence to me? when did we discuss the usage of 대해???
The core sentence is 그들은 대화해요 "they have a conversation/dialogue". 책에 대해 provides the topic: "about (-에 대해) a/the book (책)". Finally, we have a subclause which further describes the book: "about (-에 대한) Korean economy (한국의 경제)".
So far so good, but why are there two different forms for "about"? The answer is that it is in fact the same word (대하다), but when you describe a noun like 책 you need the -한 form, whereas when you use it as an adverb (like here, describing 대화하다), you need the -해(서) form. The reason for this is that the Korean equivalent of "about" is technically not a preposition but an adjective 대하다 (you can think of it as literally meaning "concerning" or "dealing with" if that makes it easier). Therefore you need to use the -ㄴ ending in front of nouns and the -아/어 form (which for verbs/adjectives in -하다 is -해) if you want to use it as an adverb.
Navers Translation makes more sense, at least in English. "They talk about books about the Korean economy."