To instal the HD textures and japanese language you'll have to:
"6F0F78A390F33E1814590891624220186714010743" (Japanese voice)
"CF6DEC0DC65B01DFF9F1597CE58C8A05626FE3D543" (HD texture)
from the DVD2 using Xbox backup creator or Exiso.
You can find them in this path: content/0000000000000000/FFED2000/FFFFFFFF/...
Now copy the files in the game directory on HDD in this path: HDD1/Content/0000000000000000/43430814/00000002/...
HD textures are automatically activated, for japanese voices go in the game options and select them.
The "00000002" directory may not be there, then you'll have to create it.
If you have the game on external HDD and this metod doesn't work try to create the directory in the HDD1 path (this metod worked for me).
Sorry for bad english