It is really cool when you can see large list of languages in the footer of Magento administration. You might think that all those languages you can see are available by default, but that is not the case. What to do when you need only two? English and Spanish for example? What seamed to be a simple task, turned up to be quite challenging.
Mage_Core_Model_Locale_Config has protected property $_allowedLocales containing array of locales that will be used to show language dropdown.
I have failed to rewrite that class, but that would be bad idea anyway, mostly because I don’t have time to spend half day testing if that has any sideefects that I’m not aware of, so here’s what I came up in the end.