"Mskiti" comes from Arabic مَسْجِد (masjid, “mosque”, literally “place of prostration”, from the verbal root سَجَدَ [sajada, “to prostrate, bow down”]), probably an old borrowing from a non-Omani dialect (compare Egyptian Arabic مسجد (masgid)).
It also accepts "masjids" for the English translation.
Are the people of Kenya and Tanzania Muslim?
Some are, some are Christians and some follow traditional beliefs.
In Spanish, it is "mezquitas". As a curiosity, when the first Spaniards arrived to the Americas, they called the local temples "mezquitas".