Just in case you're wondering, it's not completely accurate to say that Watteau was a Flemish artist. Okay, I know what you're thinking: "Of course he's not Flemish - he was a French Rococo artist!" You're right. But I bet I'm not the only person who once learned that Watteau was Flemish. To clarify: Watteau was born in the town of Valenciennes, which originally was a Flemish town. However, the French took over the town about seven years before Watteau was born.1
Does this change my belief that Watteau was influenced by the Flemish master Rubens? Of course not! There's no doubt that Watteau was interested in the Flemish masters, and I'm quite sure that Valenciennes maintained many Flemish customs and traditions, even after the French gained control.
I guess it's possible that Watteau considered himself to be Flemish, since his father was of Flemish descent. Watteau's interest in Flemish art suggests that the artist was interested in his heritage, to say the least. But if one wants to get technical, I think it would be most correct to say that Watteau had Flemish ancestry, but he was born on newly-acquired French soil.
In my mind, that means Watteau was French.
1 Emma Barker, Nick Webb, and Kim Woods, eds., The Changing Status of the Artist (London: Yale University Press, 1999), 233.