Current Locale
The following command will list your current locale
locale
Changing locale
One time
To change the locale of an app to Japanese just once run the following
LANG=ja_JP.UTF-8 LC_ALL=ja_JP.UTF-8 LC_MESSAGES=ja_JP.UTF-8 LANGUAGE=ja_JP.UTF-8 app-command
Paths
Translation files generated by applications are usually installed in the following directory, where LANG is the language code such as ja
or en_GB
/usr/share/locale/LANG/LC_MESSAGES/APP_NAME