how did they communicate actually?

Better a fool then a full-blown condescending ass-troll (which you very much are). How about you back up, attempt to put on some semblance of dignity, and try again. I predict you won't, but at least an attempt is now made to save your measly online soul.

It wasn't necessary to get that personal and that insulting. A simple, respectful correction would have done nicely.

Nothingtodotoday, this is a very rude and facetious reply from someone who obviously does not comprehend what he/she reads. When Sigrath referred to "English" she used quotation marks which indicates that we know they are not really speaking English other than so the English speaking audience can follow. The question was what language did they communicate in and is a valid one. English as we know it today did not exist and none of us would understand the mixture of Anglo Saxon and Norman French spoken in the 12th century. Given the world wide hostility to outsiders found in most cultures, effective communication would have been essential. When Marco Polo first arrived in the far east he would not have been speaking much Chinese or Mongolian. Presumably he found someone who could help him learn the basics, and that is what they would have used until he became more familiar. Perhaps it was the local orphan or lover of the hitherto unknown West who always seems to attach himself to foreigners in American films.

Thanks for your answer!

That's very interessting. I was thinking of Latin, but was not sure. Especially because I don't know who was able to learn Latin. As I think it was a privilege for scholars or monks, wasnt it?

So what you say is, that royals (and of course scholars/monks) spoke Latin, right?

So in case of Marco Polo, Marco Polo was the one who learned a foreign language to communicate with the Monogolians for example.
That must have been quite a challenge, I guess.

Halfnormal may be on the right track. On the trading routes like the silk road, there were several trading languages, based on whatever was your primary trade. Hebrew was another common trading language. That is why, for example, Christopher Columbus took Jews with him (Luis de Torres) when he went on his voyage. Persian, Greek, Arabic, Turkish and Hebrew were the languages of trade, and if you had a command of these, you could probably find someone to communicate with in almost any trading city along the trade routes.

Imperial armies also tended to develop a common language so that all soldiers could understand each other. But the Mongolian Army wasn't "democratic" like the Roman Imperial Army. It fought along ethnic lines, so it is unlikely that they developed a universal soldier's language like ancient Rome.

My experience living in Italy tells me that at the time of Marco Polo, people from the next hill over were almost unintelligible. Even now, in the early 21st century, I live on the border of 4 dialects, and I can barely understand any older dialect speakers of the more rural dialects.