How do missionaries communicate to people in foreign countries without previous exposure?

It is accepted by church tradition that St. Thomas the Apostle *somehow* came to India, but it is unclear to me how he managed to get through the language barrier. Did India have any contact with the West at this time? Could St. Thomas have an interpreter or something to ease the language barrier? Broadly speaking, how do missionaries do missionary work without previous exposure to the people's language? Can missionaries just communicate the gospel using body language or pictures?