Internationalization and localization means making your site usable in more than one languages. Well, to be honest, you could call a site that's only in english localized to english visitors too, but in any case...
These two are also known as I18N and L10N. Can you guess where these acronyms come from? The first and last letter from each word and then the number of letters between... Someone's been feeling really creative
While PHP has an extension for GNU Gettext, which can be used for localization, it isn't the easiest thing to use. Additionally, PHP can also do number and money formatting based on the locale, but this depends on the server: You must have the locale installed on it. On Shared Hosting accounts, some locales may be unavailable and you may not be able to install them. Not to mention that gettext can be a bit of a hassle to get working.
So, rather than using PHP's native support, why not use Zend Framework's Zend_Locale and Zend_Translate? Read the rest of the post at codeutopia.net