In the movie The Two Popes (2019), the two popes speak to each other in English. Does this reflect reality or was this done just for the movie? (It seems that in the actual brief footage, they speak to each other in Italian instead.)
According to this article, Francis doesn't speak English particularly well, though he understands it.
“What has always caused the most problems for me has been English, especially the phonetics.” The reason, he said, is because he’s “tone deaf.”
However, he's proficient in Italian and prefers to use it in public duties.
Benedict and Francis share also a command of Spanish, German, French, and Latin. However, given the nature of the popes' interactions, I imagine the language they most likely spoke was, as you note in your question, Italian.