Apologies if this has already been discussed. Just something that occurred to me:
Revelations marks the first time Ezio has been outside Italy. What language will he use to communicate in Constantinople? Surely most people there don't speak Italian, and since Ezio has never traveled outside his own country before, he's never had the need to learn another language.
Sure, there were a couple of missions in Brotherhood where you went to Spain, but since you were fighting Cesare's armies, it made sense you could understand what they were saying, after all they were Italians too.
In AC1, Altaïr could most likely understand Arabic and English. Whenever you encountered German, Turkish or French soldiers, their dialogue was not translated, meaning Altaïr probably didn't understand those languages. It seemed realistic that not everyone around you "magically" spoke your language.
Ezio, so far, has always been surrounded by other Italians. In the Revelations demo we see Yusuf talking to him. Does this mean Yusuf speaks Italian? Why? Or does Ezio speak Yusuf's language? If so, where did he learn it?