@vsell, it would be great to have Japanese language pack.
@Tomcraft, You could try to setup XOOPS and the lang_tool module. The module provides an interface to help you translate XOOPS modules online based on the source language, usually English, you select.
Then just copy modified eCommerce Shopsoftware/lang/english/ to xoops/modules/xtc/language/english/. Change the language folder setting through admin interface of lang_tool and start to create a new language pack based on English.
You could also update the existing language packs if you figure out how it works.