Design, art and architecture have always been key ways in which geographical regions have constructed unique identities for themselves. Antoní Gaudí was a proud Catalan, who was once prosecuted for defying an edict banning the speaking of Catalan in public. His beautiful buildings in and around Barcelona give the region its own distinct feel.
Gaudí is now probably best known for Casa Batlló, Casa Milà and Park Güell, though the Sagrada Família is widely considered to be his greatest masterpiece. You can read about Gaudí's unique take on Art Nouveau in Clive Edwards' entry on Modernismo in the Bloomsbury Encyclopedia of Design, and to appreciate his work in context, see Victor Margolin's writing on Spain in the World History of Design.
Read about nationalism in European design in Ethan Robey's article on Romantic Nationalism, or see Breward, Fisher and Wood's edited collection on British Design for more on the United Kingdom especially. Mark Mussari's Danish Modern looks at how the international modernist movement evolved in Denmark specifically, and the World History of Design has many articles on related themes, including nationalist design in Poland, regionalism in Uruguay and international consumerism in Shanghai. Javier Gimeno-Martinez's important book Design and National Identity explores the complex cultural contexts of a range of designed objects, including red telephone boxes, teapots and stamps.