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.
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.