"When is he coming?"
Swahili originated on the coast of both Tanzania and Kenya, as far south as northern Mozambique and as far north as southern Somalia. It doesn't belong to either country more than the other, it's just that the standardised form of written Swahili was arbitrarily chosen by European colonisers to be the dialect spoken in Zanzibar city. It could easily have been the Mombasa dialect that was chosen to be the standard. Also, for political reasons, Swahili was really pushed in Tanzania, so more people speak it than in Kenya, but neither of these two facts mean that Swahili belongs any more to Tanzania than to Kenya.