Also, according to the ESADE Web site there are three groups in every MBA class. Two of them are taught compeltely in English. The other one is tought with some classes in English, some in Spanish (that's the "bilingual" track). I think you will stay with that same group through all of your core classes (which make up the first few terms). But, you will be mixed up when you get to the elective courses, which you take toward the end of the program once the core classes are complete. It sounds like the program is exactly the same, the language of instruction for some of the classes is the only difference. A larger proportion of the bilingual track classmates will likely be from Spain or Latin America. But you will still get to interact with people from other parts of the world in school-wide events, and in your elective classes.
If you really prefer to be in one of the English-only groups, you should ask your contact at ESADE whether it is possible to switch!
Here is the information on languages from the ESADE Web site:
http://www.esade.edu/mba/eng/the_mba_programmes/full_time_mba/full_time_programme/full_time_languages_in_the_mba