Plug-in Manager: System - Language Code
That give you the ability to add a language code and localize by country to your language pack.
Changes the language code for the generated HTML document. Example of use: One has installed the fr-FR language pack and wants the Search Engines to recognize the page as aimed at French-speaking Canada. Add the tag 'fr-CA' to the corresponding field for 'fr-FR' to resolve this.
Now, I was wondering how to do the same with older 1.5 sites (with Joomfish)?