stumbled across this on freeware world team, looks useful for some.
Allows you to quickly change and apply a different locale from the tools menu.
* Handy tool for all people involved with multilingual usage of Mozilla applications.
* Switches the accept_language preference, so complete websites will be translated. (if the http accept language header is supported, e.g. like google does)
* Switches the Spell Checker Dictionary preference. (if supported by your Mozilla application)
* Auto restarts the application in versions 1.4+ (only if needed)
* Add 3 of your own custom defined locales.
* Select from a list of ~200 locales which locales should be visible in the menu.
* Select which settings you want to switch.
* Available for Firefox 1.0 - 1.5, Thunderbird 1.0 - 1.5, NVU 1.0, Mozilla Suite 1.7, Seamonkey, Sunbird, Flock and Netscape