- How to Temporarily Switch Languages for One Application Only on Linux

To run a single application in another language (that has already been installed), use one of the following commands:

LANG=de_DE application to start any standard X application or GNOME application in German. For other languages, use the appropriate language code. Get a list of all language codes available using the locale -av command.

KDE_LANG=de application to start any KDE application in German. For other languages, use the appropriate language code.

source:http://linuxpoison.blogspot.com/2010/05/135781677519203.html