Well from what it seems, Kitty was basing this off the films and series, rather than the books. I dont know much about the books other than the dragons talked in their own lanuage and some spoke viking. In the films they were more like basic animals. You could read a wiki on the films to get an idea I guess XD 

Being GM though, you can change up the story of you'd like. Maybe a new setting, ect. But still tie it to How To Train Your Dragon through the dragon species themselves?