system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: when countries first started exploring other countries/trading with each other. How did the people understand each other?

For example: when the Arabs and the Europeans and others came to places like India and china and others. How did they understand each other? How did they learn the language when both sides didn't know each other's languages?
gpt
For starters, most trade wasn't over long distances. Most trade was with neighbours which speak a similar enough dialect to make it feasible. Or had a significant group which speak both languages.

So A trades with B, B with C, C with D, etc... and finally it ends up at the other side of the world. Trade was mostly in non-perishable items, so time wasn't a factor.

The modern concept of shipping is quite new and somewhat forced people to agree on a common language for trade (for now, English).