To set your current shell to a different language you use the bash variable
LANG followed by the language you want:
If you want to set that so its used every time add an export line to your
.bashrc for that user. The .bashrc file can be found in each user's homedir, if they don't have one you can create it:
The command locale will show you information about locale on the server. The command
locale -a will give you a list of all the locale you can use.