This is most evident in Rowling's portrayal of the two "visitor" schools in the Triwizard Tournament. Beauxbatons is a caricature of the French, at least as many older Britons perceive them: superficially attractive, concerned mainly about appearance (although to her credit Rowling did make an exception to that point later in the series, when Fleur surprises Mrs. Weasley by not breaking her engagement after Bill is badly scarred), and ultimately light-weights in every way (except, perhaps, in the field of romance). The movie accentuates this by representing the Beauxbatons student body as almost entirely female, and throws in a gratuitous mass-ass-wiggling scene which is simply ridiculous.
Likewise, Durmstrang is a heavy-handed parody of Russians and East Europeans in general. Virtually all male, sullen, buzz-cut, large, taciturn, and given to violence; the personification of the racist fantasies of some angry, graying old Briton, and an old-fashioned one at that. If they weren't school-age, I'd imagine Rowling would have made them drunks, too!
I almost wish that Rowling had included Americans in her books. Dame Agatha would doubtless once again have provided the template: quaint accents out of a 1930s western movie, combined with exaggerated New England ones from the 1890s. Ridiculous Biblical names like "Hiram", "Ezekiel", and "Jedediah". Poor taste in virtually everything. Far too much money than is good for them, and a propensity to throw that money around thoughtlessly. Ignorance combined with overweening arrogance. And I'd bet there'd be at least a touch of over-reliance on technology or its magical equivalent, as well - with a good solid comeuppance in the end, as our plucky British heroes prove that old-fashioned spunk and stick-to-it-iveness are the qualities that really matter when the chips are down.