For starters, I'd argue that the colonists were the "foreigners" and not the other way around. That being said, interpreters were vital for communication between different communities. Often these would be individuals who had lived in both European and Native American communities and thus learned the language through exposure to it. At some point the sheer number of people interacting would make multilingual individuals common, however earlier interactions would be a bit more complicated. Early spanish entries into the American Southeast relied on members of lost parties who had been incorporated into existing communities and who could then speak spanish along with the regional dialect. They would also rely on multilingual Native Americans in their own party who, whether by their own choice or enslavement, were brought along to serve as guides.

Essentially the process relied on an initial "in", once you had one bilingual individual you could then have them speak to other multilingual individuals. I know of accounts where their would be essentially a chain of translation, a multilingual spaniard speaking to a guide who could then translate and have that message itself translated and so on.