The default Moodle installation includes many language packs. A language pack is a set of translations for the Moodle interface. Language packs translate the Moodle interface, not the course content. The following screenshot depicts the front page of a site when the user selects Spanish from the language menu:

Note that the interface is being presented in Spanish: menu names, menu items, section names, buttons, and system messages. Now, let's take a look at the same front page when the user selects Tagalog from the language menu in the following screenshot:

Note that some of the interface has not been translated. For example, the month name in the calendar and some of the links under Navigation are still in English. When a part of Moodle's interface is not translated into the selected language, Moodle uses the English version.