You might use a language other than English for the same reasons you might use different varieties of English: to represent the actual words of a speaker, to make a point, to connect with your audience, or to get their attention. See how Gerald Haslam uses Spanish to capture his great-grandmother’s words and to make a point about his relationship to her.

“Expectoran su sangre!” exclaimed Great-grandma when I showed her the small horned toad I had removed from my breast pocket. I turned toward my mother, who translated: “They spit blood.”

“De los ojos,” Grandma added. “From their eyes,” mother explained, herself uncomfortable in the presence of the small beast.

I grinned, “Awwwwwww.”

But my Great-grandmother did not smile. “Son muy tóxicos,” she nodded with finality. Mother moved back an involuntary step, her hands suddenly busy at her breast. “Put that thing down,” she ordered.

“His name’s John,” I said.

– Gerald Haslam, California Childhood