A locale is a set of environmental variables that defines the language, country, and character encoding settings (or any other special variant preferences) for your applications and shell session on a Linux system. These environmental variables are used by system libraries and locale-aware applications on the system. To see the ones installed on your system, open a terminal (or press F4) and type:
Normally, a user sets the locale during installation. If that was not done, or if a change should be made, the easiest way is to use MX System locales.
Be careful when removing locales that you do not remove your own! The easiest way is to install the package “localepurge” and run it as root. (Warning: this tool is a hack which is *not* integrated with the system’s package management system, so use it at your own discretion.) The screen that pops up wants you to check the boxes of the ones you want to keep.
Alternativelym you can open a terminal and enter the command (which also wants the ones that should be kept):
sudo dpkg-reconfigure locales