This how I think this scene will go down:
Belle: Guys, I found out what Zelena wants based on the ingrediants she stole. She took David’s courage, she wants Regina’s heart, my guess is, she wants Rumple’s intelligence as well. Look here, in this book.
Emma: It’s written in Elvish.
Belle: Yeah. The whole spell is written there, along with the ingredients.
Emma: Wait, you understand this?
Belle: Uh, yeah.
Emma: When did you learn how to do that?