MozillaTranslator (
http://www.mozillatranslator.org/) is a 
L10n tool
created by a Mozilla L10n contributor, 
Henrik Lynggaard, from Denmark.
The tool is a 
Java application, version 5 and up need at least Sun JRE 1.4.x to run.
Sometimes it's a bit 
hard to configure, but once set up it's nice and easy to maintain the L10n.
It reads the files 
directly from the .jar, and is able to detect just the changes since the last update, so you only have
to look at the really changed texts. It can 
export .jar files again, and even create ready-to-install 
XPI files.
It's also capable of maintaining multiple products within one MozillaTranslator installation.