Jambo Rafiki is not a term well-known in this area.

But for Portland and John Mithen, they will be hearing a lot of the African words for “hello friend” over the next two years.

The couple, who live in Dallas, recently signed on as missionaries in Moshi, Tanzania, with The Rafiki Foundation, a Christian organization established in 1985 with the goal of helping orphaned and vulnerable children and teens in Africa become godly contributors to their communities and the world.

Portland, 1977’s Miss Texarkana, has traveled many paths involving missions, but views...