LCMESSAGES

LCMESSAGES, commonly written as LC_MESSAGES, is a locale category used by POSIX and Unix-like systems to control the language of user-visible messages produced by programs. It governs the selection of translated strings from message catalogs when applications use localization interfaces such as gettext.

Definition and scope

LC_MESSAGES is one of several locale categories defined by locale.h and the POSIX standard. Other categories include LC_TIME, LC_NUMERIC, LC_COLLATE, LC_MONETARY, and LC_CTYPE. The category determines the language of runtime messages, such as error and status strings, rather than data formatting like dates or numbers.

Setting and inheritance

The locale for LC_MESSAGES can be queried or set with the function setlocale(LC_MESSAGES, ...), or via environment variables such as LC_MESSAGES or LANG. Common values are locale names like en_US.UTF-8 or fr_FR.UTF-8, or the C/POSIX locale for a minimal, non-translated baseline. Environment variable LC_ALL can override individual categories, including LC_MESSAGES.

How translations work

Applications that support localization use message catalogs (for example, gettext .po/.mo files) organized under locale directories such as /usr/share/locale/<locale>/LC_MESSAGES/. If a translation exists for the active LC_MESSAGES setting, the translated string is shown; otherwise the original message is used.

Relation to other concepts

LC_MESSAGES interacts with other locale settings to determine overall language behavior of an environment. Not all programs honor every locale category, and some rely on their own internal localization mechanisms. Proper translations and installed locale data are required for LC_MESSAGES to have full effect.