It looks like $day contains the name of the day, and nothing else. You need to tell the program to print the "Today is".

print "Today is ";
given ($tgt) {
      when("fr_fr") { print “$day" ; }
      when("it_it") { print “$day" ; }
      default { print “$day" ; }
}
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If you want "Aujourd'hui est lundi" or "Oggi è lunedi", you need to substitute those in the line for each language.