To change the language settings of the Debian operating system, you must first run the su command and get root permissions (admin).
Run the apt-get install language-pack-xx command (where xx is the name of the language pack) to download and install the language pack of your choice and then dpkg-reconfigure locales. A window will ask you to select the language you want to use for the distribution. Make your selection and confirm.
After completing these steps, simply reboot your system to apply the new settings.