The LC_MESSAGES environment variable is used to specify the language of messages for an internationalized program. Internationalization is the process of designing and developing a program that can adapt to different languages, cultures, and regions without requiring modifications. Localization is the process of translating and customizing a program for a specific language, culture, or region.
The LC_MESSAGES environment variable is one of the several locale categories that can affect the behavior of a program. A locale is a set of parameters that defines the user’s language, country, and any special variant preferences that the user wants to see in their user interface. The locale categories are:
LC_CTYPE: Character classification and case conversion.
LC_NUMERIC: Numeric, monetary, and time formats.
LC_TIME: Date and time formats.
LC_COLLATE: Collation order.
LC_MONETARY: Monetary formats.
LC_MESSAGES: Formats of informative and diagnostic messages and interactive responses.
LC_PAPER: Paper size.
LC_NAME: Name formats.
LC_ADDRESS: Address formats and location information.
LC_TELEPHONE: Telephone number formats.
LC_MEASUREMENT: Measurement units (metric or other).
LC_IDENTIFICATION: Metadata about the locale information.
The locale categories can be set individually by using the export command, such as:
export LC_MESSAGES=“pt”
This will set the language of messages for an internationalized program to Portuguese (pt) for the current login shell and any child processes. Alternatively, the locale categories can be set collectively by using the LANG or LC_ALL environment variables, such as:
export LANG=“pt”
This will set the default locale for all the categories to Portuguese (pt) for the current login shell and any child processes, unless overridden by another LC_* variable.
The other options in the question are not correct for this task. The LANGUAGE environment variable is used to specify a priority list of languages for programs using the GNU gettext library. The UI_MESSAGES, MESSAGE, and ALL_MESSAGES environment variables are not valid locale categories.
References:
LPI 102-500 Exam Objectives, Topic 105.3: Localization and internationalization
LPI 102-500 Study Guide, Chapter 5: Customizing Shell Environments, Section 5.3: Localization and Internationalization
Locale man page
