There is a very silly and somewhat ridiculous reason why Dee, and her boyfriend Asalamalakim address Dee's family in Swahili in Alice Walker's short story "Everyday Use".
The reason is that Dee has adopted a new persona. She claims to have chosen a new Afro-centric lifestyle complete with a new name, diet, and language.
Meanwhile Asalamalakim is going through motions with Maggie's hand. [...]Asalamalakim wants to shake hands but wants to do it fancy. Or maybe he don't know how people shake hands. Anyhow, he soon gives up on Maggie.
"Well," I say. "Dee."
"No, Mama," she says. "Not 'Dee,' Wangero Leewanika Kemanjo!" [...]
"She's dead," Wangero said. "I couldn't bear it any longer, being named after the people who oppress me
This is interesting because there is really no need for Dee to do all that. She is over-doing her Afrocentrism by acquiring behaviors and mannerisms that Africans, themselves, might find a bit ridiculous. Her boyfriend Asalamalakim is no different, as you can see. He is so detached from "the moment" that he does not even want to consume the same food as everybody else.
We sat down to eat and right away he said he didn't eat collards and pork was unclean. Wangero, though, went on through the chitlins and com bread, the greens and everything else. She talked a blue streak over the sweet potatoes. Everything delighted her.
We know that Dee actually is being superficial. Culture is not the compilation of history and sacrifices of the people. To Dee, culture is found in objects, foods, names, and manners. This is why her mother has a hard time considering giving her the quilt. She knows that Dee is artificial, and not genuine like her younger daughter. Hence, the Swahili, the dressing up, the sudden love for all things "African" and ancestral are part of her artificial nature.