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 (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.
For those who want to continue learning Czech during the semester, there are of course commercial language schools, and may be other possibilities as well. The Office for International Relations will explain them to you during the Orientation fortnight.