use strict;
use Encode;
$|++;

my $t = 'thai.txt'; # contains => ต้มยำกุ้ง

open my $fh, '<:raw', $t
    or die "Couldn't open $t: $!";
my $content = do { local $/; <$fh> };
close $fh;

$content = decode('UTF-8', $content);

binmode *STDOUT, ':encoding(UTF-8)';
print "$content\n";