translated manpage included in d-i/* do not be surprised, there are only 14 pages so I could have done in a week :)
http://debian.blog.bbiq.jp/d-i-m/installer-manpages.tbz 56.4k, everything incl. original-copy/Japanese-translation/script/etc. as po4a is used to make life easier, other party can use :) -- victory no need to CC me :-)
