Just to demo "use byte" as jweed mentioned.

use strict;

my $a = chr(4000);
{
        use bytes;
        print substr($a, 0, 1), "\n";  
}

{
        print substr($a, 0, 1), "\n";  
}
[download]

You will see a warning saying "wide character in print", don't worry about that, that is what supposed to happen.