At an early point in his timeline, Julian's reaction would have rivalled Hiccup's in terms of flat-out awe. Just because similar creatures aren't rare doesn't mean it isn't amazing to meet one for the first time, especially one intelligent enough to understand speech. As it is, he's older and calmer than he once was, and his reaction is restrained to just a pleased little smile.

"Excellent. And I take it you can't speak? Or don't want to, at least... my kingdom for a medical tricorder!" He sighs, melodramatic, but it's evident from his expression and general aura of excitement that he's not too disappointed. "I don't suppose you're familiar with any kind of sign language? Or, er-- Morse code, perhaps?"

In this respect, Julian's definitely not the best person for the job. In terms of sheer unbridled curiosity (and even now, a certain level of inadvisable trust in the universe's good intentions) he's excellent for this kind of first contact, but when it comes to communicating without speech, well, he's a little too talkative. If his assumption about Toothless's lack of verbal communication is correct, that's an awful lot of questions to be asking to someone who can only answer by nodding or shaking his head.