When you want to add locale-specific resources in Android, you have to add the lowercase ISO-3166-1 code of the language to the resource folder\'s name. So far so good.
Many devices ship with a limited selection of languages in the settings menu, but can actually be set to any system locale using an app such as LocaleSwitch.
It should be pretty easy to test whether Basque is supported by adding a custom locale in LocaleSwitch and then adding the resource folder to see if the system loads the resources from this folder automatically.
Finally, Gingerbread 'support' for Catalan may only reference the inclusion of android.R values since 2.3, though I can't see them in the framework repository.