Wouldn't wearing any 'garb' from any nation in particular be considered, 'national pride'? if not, why?
Presumably it depends on intent. The kilt, jacket, sporran etc is acceptable formal wear here for black tie events as a regional variation, therefore not always worn as a symbol of nationalism. Nor is the kilt exclusive to Scotland, there are Breton and Greek versions too but they're a bit on the short side.
You might find some Witnesses that disapprove of kilts in the same way you get some that disapprove of chess as a war game.