Gettext/Setting-the-POSIX-Locale

From Get docs

2.3 Setting the Locale through Environment Variables

As a user, if your language has been installed for this package, in the simplest case, you only have to set the LANG environment variable to the appropriate ‘ll_CC’ combination. For example, let’s suppose that you speak German and live in Germany. At the shell prompt, merely execute ‘setenv LANG de_DE’ (in csh), ‘export LANG; LANG=de_DE’ (in sh) or ‘export LANG=de_DE’ (in bash). This can be done from your .login or .profile file, once and for all.

Locale Names:    How a Locale Specification Looks Like
Locale Environment Variables:    Which Environment Variable Specfies What
The LANGUAGE variable:    How to Specify a Priority List of Languages