I added a fix that we needed at Posterous. URLs like: http://foo.posterous.com/?tag=沖縄南部&page=XX always returned page=2 for any generated link past page 1. It seems that multi-byte chars were not being accounted for when replacing the '@' with the page number.
page number generation should handle unicode params like 沖縄南部
Hey, sorry this hasn't got any attention. I didn't pull the change because it requires mb_chars and will_paginate supports Rails versions that are older than multibyte features.
However since people don't seem to run into this problem, I'll close this right now without fixing. The new will_paginate for Rails 3 doesn't suffer from this bug, anyway.