The Russian word for this city is actually closer to Moskva. We’ve had a number of threads about how other peoples’ names for their own country is typically different from the names that other countries ascribe to them, but for the most part we keep city names as close to the original as possible.
So. . .
Who started calling it Moscow? It has a Polish look to it, so did the Poles vault this version into prominence? And, if so, who decided that it should “officially” be pronounced “moss-ko,” as opposed to “moss-kow,” since that’s not even how the Poles (assuming they’re the culprits) would pronounce it.