[pseudalopex]

I think the norm is the current surroundings, not wherever the subject is from. Dr. Smith is Smith-sensei in Japan. The New York Times is known for its use of courtesy titles, and it calls knights "Mr.".

Pope is a high office, and Francis is his chosen name. It would be rude of you to call him by his birth name; it would be rude of him to insist you call him "Your Holiness", although you probably should if you're visiting the Vatican.