Do missionaries have to live like the people they are working among?
Yes. Missionaries have to live like the people among whom they work when entering a foreign field. They cannot simply live with Western culture, habits, and food, because doing so would keep them from reaching or touching the people. Paul's example of becoming all things to all men so he might save some illustrates this.
Les explains that every missionary learns quickly in a foreign field that they have to live like the people amongst whom they are working. They cannot just come in and live with Western culture, Western habits, and Western food; if they did, they would never touch anybody. He points to Bill and his wife, whose daughter is in mission work down in Peru, and to years of contact with missionaries. This fits the passage's principle: Paul became as under the law to those under the law, as without law to those without law, and as weak to the weak, making all things to all men that he might save some. Paul never forsook the morality of God's law.
To the weak became I as weak, that I might gain the weak: I am made all things to all men, that I might by all means save some.