Japanese Language

A good facility with reading, writing and speaking the Japanese language is a prerequisite for studying at an animation school or working in an animation company. The same goes for working in a manga studio. All instruction in animation schools is given in Japanese and very few of the teachers will have any English language ability at all. There are also not many staff members at animation companies who have any understanding of English. A company will be very unlikely to hire anyone with poor Japanese language skills and a school may refuse admission outright.

 There is no read measure of how much time someone needs to study Japanese before he/she could work or study. I would strongly suggest a year of Japanese - in Japan - before attempting to enter an animation school. Studying Japanese outside Japan can be an OK start but it is impossible to learn the language to a level where you can communicate easily in it unless you live in Japan. Unless you are in a very intensive course the best you can hope for from Japanese language classes in a foreign country is to build vocabulary and understand the grammar. It would take around two years in country for someone to get to the level where they could work at an animation company without major communication difficulties. Most universities suggest two years of study before entering school.
There are a lot of Japanese language schools in Tokyo. Here are some that I found listed in local magazines. (I am not recommending any of these and I have no direct contact with any language schools but these may serve as a starting point.)

Please take a look at this article before checking into the schools.