"Tunaandika somo la kiswahili"
Translation:We are writing a Swahili lesson
I think I might write "a lesson on Swahili" if I was going to teach the linguistic theory of it rather than teach students to speak it ("a Swahili lesson").
But I think Ivoryblossom must be right: "write" is the wrong translation here. It should probably be "We have a Swahili class."