This is a question I had since I was a child and I didn't know where to post. In ancient times, I have read that many invasions used to take place and people with completely different cultures and languages used to interact with each other. For example, Alexander's invasion of India. My question is, how did the first Greek, for example, converse with the first Indian? The two are almost completely different. How did they understand each other? How did they translate each other's language given they had no prior knowledge of each other's language?
For example, I looked up in Greek, water is called 'nero' and in Sanskrit water is called 'ap'. So when the two met for the first time, how did they come to know about when the other was talking about water? Did they use sign language of some kind? How did they eventually know complex words like emotions, feelings, expressions, etc?
Generally speaking, language barriers weren’t as big as people tend to assume they were. Chances are that before meeting, they will already share a mutual language, or know someone who knows both, so they were able to communicate with each other through some lingua franca. Trade networks were large and complex enough that there was bound to be a middleman of some sorts to ease communications.
More can be said if anyone wishes to add something new, but in the meantime you may enjoy reading:
and more from the FAQ section on Cross-Cultural Communication.
In situations like Columbus—an unusual and unlikely instance where neither group had heard of the other and there was a language barrier at first—then immersion effected language learning: signing, gesturing, context clues, pantomiming, etc. helped people build a vocabulary that let them communicate, verbally and physically (sometimes, if necessary, actions spoke louder than words). Someone was eventually able to figure out the other's language, and they were able to serve as a translator. I don't have details on specific incidents of language learning in these situations (maybe someone can pop in with that), but if you can imagine someone approaching you, mimicking the action of eating, and you pointing them where to find food and they do it—or perhaps, someone pointing to trees and saying the word feshith until you figure out that's the word for tree, and then you continue learning when they point to water and say eveth—you can understand the basics of how people without a shared language were able to communicate. It's essentially an elongated, more complex version of that process.