Was just considering this; in cases where traders, merchants, explorers, etc from far off lands arrived in new, unfamiliar territory (European merchants arriving in India and China for the first time, for example), how did they communicate? How was the problem of the language barrier overcome, and were there any notable mishaps or incidents from misunderstandings or significant cultural differences?
There's always room for discussion, but perhaps the section Cross-cultural communication and lingua francas from our FAQ will answer your inquiry.