Localization means that an application (or homepage) can be used from different users which speak different languages. But as you already have expected Localization means more than only translating strings. It includes
Zend_Locale- Backend support of locales available for localization support within other Zend Framework components.
Zend_Translate- Translating of strings.
Zend_Date- Localization of dates, times.
Zend_Calendar- Localization of calendars (support for non-Gregorian calendar systems)
Zend_Currency- Localization of currencies.
Zend_Locale_Format- Parsing and generating localized numbers.
Zend_Locale_Data- Retrieve localized standard strings as country names, language names and more from the CLDR.