THE glitz may have migrated to the French Riviera, but Biarritz doesn’t need it. The posh seaside town in southwest France is enjoying a renaissance, as people discover the appeal of this aristocratic resort on the Bay of Biscay where worlds collide and expectations are upended. Once the reigning vacation spot for Europe’s noble and gentry classes, Biarritz’s golden shores are now shared by everyone from bronze beauties in designer sandals to drop-out surfers in frayed flip-flops. Even the languages are mixed up. Walk into any of the town’s creaky old bars, and the patrons might strike up a conservation by saying a few words in rapid-fire French, Spanish, English or even Basque, the local language that, like the resort, is in a class by itself.