Language learning and translation sharply increased with any “discovery” of new people. There are many driving factors as to why— but it seems that curiosity as well as the fervent need for social interaction among humans has made language a permeable barrier.

Discovery” of any new people/new language is and has always been met with study and translation. In almost every circumstance there is an immediate need to understand it. That need may be driven by trade, war, personal reasons or anything in between. I guess this has been a long winded way of saying that Humans will always develop a means of communication.

The short answer to your question, though not a very comprehensive one is: How: through immersion and study. When: since humans began speaking.

I recently answered another question regarding language which you may find useful.