>perl -wMstrict -le
"my %xlate = (
   'string a' => '3',
   'string b' => '2',
   true       => '1',
   false      => '0',
   tt         => '22',
   ttt        => '33',
   );
 my $xl = join '|', map { quotemeta } reverse sort keys %xlate;
    $xl = qr{ (?i) \b (?: $xl) \b }xms;
 ;;
 my $s =
   'vv TTT ww TT String A xx sTrInG b xtruex True yy FALSE zz';
 print qq{'$s'};
 ;;
 $s =~ s{ ($xl) }{$xlate{ lc $1 }}xmsg;
 print qq{'$s'};
"
'vv TTT ww TT String A xx sTrInG b xtruex True yy FALSE zz'
'vv 33 ww 22 3 xx 2 xtruex 1 yy 0 zz'