Do I need to speak fluent Polish?

You do not need to because universities offer a large variety of study programmes in English. Nevertheless, you may learn Polish either for private everyday use for the time you stay in Poland, or for joining a university course in Polish. Courses of Polish language and culture or survival Polish with orientation programmes are organized by most universities hosting foreign students. This type of course can last for a few weeks just before the academic year or can run throughout the whole semester.
In case you choose Polish as the language of your studies, however, you will be required to prove your proficiency in Polish before you start your studies. Foreign students wishing to pursue studies in Polish are required to have a command of Polish, allowing them to understand lectures and other forms of tuition at universities see www.polonicum.uw.edu.pl. 
Information on Polish language certificates is provided by the State Commission for Certification of Command of Polish as a Foreign Language (www.buwiwm.edu.pl).