For instance, when the Spanish first sailed to the new world, how did they make deals with the natives? Or when the Portuguese landed in India, how did they communicate with the locals?
This is probably worth asking over in /r/askanthropolgy or /r/asklinguistics
You can aslo see previous answers to similar questions in /u/drylaw response to https://www.reddit.com/r/AskHistorians/comments/b9pqhk/when_hernan_cortez_and_the_spaniards_arrived_in/
Or /u/bamabreeze505 response to https://www.reddit.com/r/AskHistorians/comments/9ysb2j/how_the_first_translators_learned_other_languages/
Or /u/tglucose response to https://www.reddit.com/r/AskHistorians/comments/8rs3z2/how_long_did_it_take_to_overcome_the_language/ (he also suggests further reading via Empires of the World: A Language history of the World by Nicholas Ostler)