The Message Facility consists of standard defined subroutines and commands, and manufacturer value-added extensions to support externalized message catalogs. These catalogs are used by an application to retrieve and display messages, as needed. The following Message Facility subroutines get messages for an application:
| catopen | Opens a catalog. |
| catgets | Gets a messages from a catalog. |
| catclose | Closes a catalog. |
| strerror | Maps an error number to an error-message string appropriate for the current locale. |
For more NLS subroutines see "List of National Language Support Subroutines".