Aswell as things like Marco Polo and John of Plano Carpini visiting them. How did they communicate and more generally, how did anybody communicate with other peoples during invasions and diplomatic missions at this time and earlier? What was protocol?
I posted this yesterday so I hope nobody minds me reposting as I didn't get a single response last time.
Follow up- I've heard that yelu chucai has exaggerated his role in the Mongol politics in The Secret History and that his name does not really appear in the list of dignitaries in the Mongol Empire, and that stories such as him convincing Genghis Khan not to turn Northern Chinese farmland and cities into grazing pastures may not be entirely true. What's the academic consensus on Yelu Chucai?
In Marco Polo: From Venice to Xanadu by Laurence Bergreen the author explains that Marco Polo, as well as his father and uncle, picked up the language in the years that they traveled and traded there. So, in the case of Marco Polo, he spoke the same language as the Khan, or at least as some other officials.