Installing an extension with more than one locale

Hi,

I've been creating an extension for mozilla thunderbird. I've created 2 
different install.js versions.

1) the first version registers only one locale (the user is able to 
choose the locale, when installing the extension). In this case 
thunderbird uses the correct locale for my extension.

2) the second version registers all locales, when installing the 
extension. In this case only the extensions en-US files are used by 
thunderbird. I'm able to switch between thunderbirds locales, but not 
between my extensions locales! The extension everytimes uses en-US. WHY?

Any help?