As far as I know, there's no requirement for the visa (official document in the passport to be able to enter the country) itself. But check with the embassy of your country to make sure. However, to able to enroll into a university, there may be a required proficiency level, usually B1 or B2. That depends on the university and on the field of study, however. Check the webpages of the university you want to apply to.

And I would like to add, that most universities offer intensive courses for foreign students. Sometimes they take place during the weeks before a semester starts, so that you can prepare yourself in advance. Lectures in English get more and more common as well.