You have to pass a special proficiency test to attend university in Japan as a foreign student. Of course univerisities with courses taught in English would deem that unnecessary, but those are rare. You can study Japanese in Japan until you pass the proficiency test, but even then university studies in a second language are always going to prove difficult because you simply don't have the same background as the other students.
Here is the test you need to take
EJU-JASSO.