Updated Japanese translation, thanks to Toshihiro Takehara.
Squashed commit of the following:

commit 4a821ff85298f3804dc9294740890099abe843e6
Author: Toshihiro Takehara aka nouphet <nouphet.ratanavong@gmail.com>
Date:   Wed Mar 19 02:56:27 2014 +0900

    Add some translation for Japanese.