The natives of Barcelona are Catalans, a distinct type of Spaniard (that is, if they allow you to call them Spanish).
Catalans are known for being extremely proud of their regional identity, culture and language, and if you know a bit of Barcelona history it’s easy to understand why. Catalonia did not form part of ‘Spain’ as we think of it today until Ferdinand of Aragon married Isabel of Castile in the late 15th century. Before that, the region was prosperous in its own right, especially during the Middle Ages, as is evident Barcelona’s intact Gothic Quarter and old port.Dwarfed by the rise and fall of Spain’s great imperialistic exploits, Catalonia did not really come to the forefront of European society again until the 19th century, due to an industrial, demographic and artistic boom. Movements for regional independence strengthened in this period, and Catalonia briefly gained autonomy during the 2nd Republic, the democratic government that preceded the Spanish Civil War. When Francisco Franco’s armies defeated the Republicans in 1939, the defeat was felt even harder in Barcelona. Franco banned the Catalan language, changed street names from Catalan to Castilian, and abolished the regional government, the Generalitat, among other forms of censorship. This endured in some form or another until Franco’s death in November of 1975.
Catalans have since reclaimed their language and reestablished the Generalitat. Barcelona is a bilingual city, with a culture distinct from the rest of country. There’s even a statute pending debate in the National Congress which would grant Catalonia the title of a “nation,” among other privileges, though its approbation and terms remain to be seen. This "Estatut" is sure to mark a new, important era of Barcelona history.
SO, be prepared to hear Catalan all around you and remember that it is truly its own language, not a dialect of Spanish. All that said, don’t worry about the language barrier if you want to study Spanish in Barcelona. Everyone is completely bilingual and most signs are in both Spanish and Catalan. While Barcelona natives are very proud and dedicated to maintaining their local culture, you should have no problem getting integrated as long as you respect their pursuits… and it wouldn’t hurt to educate yourself about the region if you’re planning on a longer stay!