Which variable is critical for ensuring that the correct language and region settings are applied in a Linux session?

The variable that plays a critical role in ensuring that the correct language and region settings are applied in a Linux session is LC_ALL. This environment variable overrides all the other locale-related variables, such as LANG and LC_* variables, for all locale categories. When LC_ALL is set, it ensures a uniform application of the specified locale across all aspects of the system, making it the most straightforward way to change the locale settings.

Using LC_ALL is particularly useful when you want to enforce a specific locale configuration without needing to declare multiple individual variables. For example, if you set LC_ALL to "en_US.UTF-8", it will apply this English language and US regional format for all categories, including character classification, collation, date formatting, and more.

In contrast, while LANG provides a default locale setting, it can be overridden by more specific LC variables. LANGUAGE is used to indicate a list of language preferences but does not enforce them across all settings. LC_MESSAGES specifically handles the language for system messages but does not influence other locale-sensitive behaviors. Therefore, setting LC_ALL is the most comprehensive approach to ensure that the correct language and region settings are consistently applied across a Linux session.