The short answer is, “It depends on the program.” For example, if you want to attend Japanese-language programs starting in April as an international student, you must demonstrate your proficiency by submitting a test result indicating you passed at least N2 of the Japanese-Language Proficiency Test (JLPT), or you are required to take the Examination for Japanese University Admission for International Students (EJU), a test to assess your Japanese language skills and basic academic proficiencies.
Many colleges and universities today offer admission options that do not ask you to prove your language proficiency. To increase the number of international students to offset the small pool of Japanese applicants, these schools provide programs in English. Unless you are from a country where the language of education is not English, you don’t need to submit proof of your English ability.
Still, learning Japanese before going to Japan is a great idea. Even if you have no problem on campus, you need some language skills to be successful in the larger community. After all, your job opportunity can hinge on your fluency in Japanese.