The working Language at our faculty is Catalan. Most of the courses are given in Catalan. Though many lecturers will change into Spanish when they have Exchange students in their class, you should know it depends on the lecturer and be aware of the bilingual reality here.
Each semester the faculty runs a free basic Catalan course for foreign students of any degree, which awards 1,5 ECTS. To avoid timetable clashes with other subjects, it's compatible with most of the classes.