# ...
my %regex;
@regex{ keys %hash }= map { qr/(?<!\S)\Q$_\E(?!\S)/i } values %hash;

foreach my $string ( @strings ) {
    foreach my $key ( @keys_sorted_by_length_desc ) {
        if(  $string =~ $regex{$key}  ) {
            print "Found '$key' in '$string'\n";
            last;
        }
    }
}