To the best of my knowledge Normandy was settled by treaty by the "Northmen" under Count Rollo who was enticed by the French throne to give up 'viking' in exchange for land, title, and a duty to guard the coast against others of his kind. I don't recall the year this agreement was reached, perhaps some other kind person can fill in that gap.

By 1066, yes they spoke French (ish). It was Old French, we wouldn't recognize it today, and it was undoubtedly a dialect. From the first day of the Conquest, French was the language of the Court and Nobility in England. Since MTW begins only a short time after the Invasion, I've always wondered why England didn't have more Loyalty problems. The general populace is still Anglo-Saxon, and resentful of the invaders but this doesn't seem to be portrayed in the game.

Also worth noting is that Sicily in the game is also a Norman Kingdom, only recently founded, and that at the time the game begins, has just come within a hair's breadth of destroying the Byzantine Empire. Both Siciliy and England are nominally subject to the French crown at this time, though this fact is convienently ignored in most situations.

As a further note, having spent some time in the Norman countryside, I can say that at least some Norman's today don't like being too closely associated with France and are very proud of their seperate heritage.