Though people in Barcelona speaks Catalan, Spanish is readily understood. However, there is definitely a faction that would like to imagine Spain as nonexistent--indeed, there was graffiti to that effect in more than one place. The architecture is, of course, amazing, as are the beaches, though they're terribly crowded.
Quick Tips:
You'll love walking down Las Ramblas and stopping to sit on the benches for some people-watching.
Stop by La Boqueria for inexpensive fruit and vegetables.
Visit the Olympic village--it's a beautiful and relatively uncrowded area.
Eat paella! Delicious!
Best Way To Get Around:
The metro is cheap and easy, as is walking.