Here's a breakdown:
* Catalan: This is the co-official language of Catalonia, the region where Barcelona is located. It's spoken by a large majority of the population, and you'll hear it used in everyday life, government, and media.
* Spanish: As Barcelona is in Spain, Spanish is also widely understood and used, particularly in official settings, commerce, and with tourists. Many people in Barcelona are bilingual.
So, while Catalan is the dominant language in Barcelona, you can get by with Spanish, and many people will be able to communicate in both languages.