A locale is a complex of an application's interface captions and messages in a certain language. In POA, a set of files containing the interface messages for all available Control Panels and system component interfaces localized in a certain language is called a Language pack. One can install a language pack to see all text information in POA translated on his/her language.
POA has a built-in mechanism of managing language packs. You can add new language packs provided by your vendor or edit the entries of existing ones. Original language packs provided with the system come in the form of POA packages. If there is more than one language pack installed in the system, a user can select an interface language at the login screen. You can see the list of available languages at Top > System Director > Configuration Manager > Internationalization & Localization.