If you want to follow a full course of studies in Czech, of course you have to learn Czech before starting. If you are coming to Prague for a year or a semester as an Erasmus or other exchange student (Short-Term Studies), you do not necessarily have to learn Czech because we offer enough courses in English (and a few in German). But our experience is that the more Czech you learn, the more you will get out of your stay in Prague.
For those on the Short-Term Studies course, the Office for International Relations organises a short (10 x 4 hours) introductory course to the Czech language as an optional part of the Orientation fortnight in September. Usually there are follow-up courses at the Faculty for those who want to continue learning Czech during the semester, and of course there are many commercial language schools in Prague as well.