I study at RCM, the state university. There are 4 LCME accredited schools in Puerto Rico which include RCM, PSM,UCC and SJB. In RCM some lecturers give the lectures in English and some in spanish. It depends on the nationality of the lecturer. All of the powerpoints are in english,you're tested in english and the textbooks are also in english.
You do need some basic spanish skills, to talk to patients etc. But if you ask a spanish speaking proffesor in english I'm sure they'll reply to you in english...
Hope this helps a bit, if you have any questions feel free to ask.