Spanish (español) is the national language and is understood almost universally in Barcelona. However, Catalonia's native Catalan language- a mixture of French, Spanish, and the other Romance languages- is spoken by roughly seven million people. The language was discouraged at points in history, but the 1975 death of Franco allowed the region of Catalonia to gain autonomy and be declared an official language. Today, many street signs, landmarks, and menus are marked in both the national language of Castilian as well as the Catalonians's own regional language. About 95% of the population understand Catalan, 74.6% speak it, 75% can read it, and 47.1% can write it.
The Royal Spanish Academy (Real Academia Española or RAE) is the institution responsible for regulating the Spanish language. The Institute for Catalan Studies (Institut d'Estudis Catalans or IEC) is an academic institution which seeks to research and study all elements of Catalan culture. It works to standardize the Catalan language and is based in Barcelona.
The percentage of Spaniards that speak other languages is every increasing, but the need to speak Spanish - especially Catalan - is helpful. There are full-time and part-time courses, as well as residential courses (where they offer accommodation). Most offer sample lessons or let you sit-in for free before signing up. Shop around before choosing.
Private lessons are another option. More expensive than language courses, these can be especially effective. Expect to pay between 10-20 euro per hour depending on the tutor's qualifications and experience.
You can search for opportunities in a local newspapers, on message boards at pubs, copy centers, supermarkets, universities, and cafes, or on online boards such as EasyExpat's classified's or Job Listings for tutors and classes. You can also find friends on the forum to work on language exchange.
An exchange partner is an excellent resource for practicing a new language with a native speaker. As an added bonus, language exchange partners can help you understand the culture of the area and inform you of local happenings. Questions about gift giving, festivals, nightlife, and greetings can be addressed without worry. In the best case sceneries, an exchange partner is not only your ambassador, but a friend.