We have more than 300 hosts, and are adding new hosts almost daily. Hosts are spread all over Japan. Many speak English and welcome non Japanese speaking people. Hosts can be all kinds of places.  Many hosts accept WWOOFers all year round, provided you have a visa, and anyway, many are situated in warmer parts of Japan, so WWOOFing all year round is fine.  Neither we at the WWOOF Japan office nor our hosts can in any way support regarding visa matters.