That should be simple, there should be language.en file in each basepak.pk3 (for each game), probably it should be substituted by language.it or whatever; then edit its contents.
Then, start the game with following cmdline parameter:
OR use this command in console:
ID is extension of 'language' file. (In your case it should be +language it)
Already tried that, working fine.
Ofcourse this will only work with those characters, that are put in graphical font.