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