For many computer users, a foreign language is still an insurmountable barrier. I've come across opinions like: "maybe I'd try this Linux thing, but it's in English". Well, no. Linux speaks Polish, and has for a long time.
For this we install and configure the locales package
#installation as root
aptituide install locales
#then we configure our package, selecting pl_PL.UTF-8
dpkg-reconfigure locales
#installing Polish fonts
aptituide install fonty-rg
#we download manuals in Polish
aptituide install manpages-pl

We need to decide whether we're localizing Linux globally or locally (for a specific account) : export LC_ALL=pl_PL.UTF-8
export LANG=pl_PL.UTF-8
export LANGUAGE=pl_PL.UTF-8 GLOBALLY: we save the three "exports" above to the /etc/profile file
LOCALLY: we save the three "exports" above to the .profile or .bash_profile file in the user's home directory

The last step is to log back into the system.