Although Japanese is spoken almost exclusively in Japan, it has been and sometimes still is spoken elsewhere. When Japan occupied Korea, Taiwan, parts of the Chinese mainland, the Philippines, and various Pacific islands before and during World War II, locals in those countries were forced to learn Japanese in empire-building programs. As a result, there are many people in these countries who can speak Japanese in addition to the local languages. Japanese emigrant communities (the largest of which are to be found in Brazil) sometimes employ Japanese as their primary language. Approximately 5% of Hawaii residents speak Japanese, with Japanese ancestry the largest single ancestry in the state (over 24% of the population). Japanese emigrants can also be found in Peru, Argentina, Australia (especially Sydney, Brisbane, Melbourne and Cairns), the United States (notably California, where 1.2% of the population has Japanese ancestry, and Hawaii), and the Philippines (particularly in Davao and Laguna). Their descendants, who are known as nikkei (日系, literally Japanese descendants), however, rarely speak Japanese fluently after the second generation.
source : wikipedia