Thank you everyone for your comments.
Welcart has usces-ja.mo. However not all the materials have been internationalized yet and there are several things noted in Japanese directly on the code. Therefore, you should be aware of the fact that there might be some Japanese parts appear without translation by gettext.
Official Wellart POT file is not yet prepared. You can use usces.pot in the languages directory instead.
Japanese version of MO file has been done with poEdit.
The file names of MO file and PO file is following.
usces-**.po
usces-**.mo
(** is the language code)
The file is in usc-e-shop/languages/.
* notice
Welcart are tailored to the business practices of Japan. Therefore, for use in countries other than Japan, there might be some items, such as names, addresses, and date, set awkward way for their habits.
We are currently working on solving this problem. In new system, you will be able to choose an American business practice instead for other countries. When we finish these processes of real internationalization, we will, by this forum, announce you and ask for language file to bundle on Welcart.
Your help will be appreciated then,