STDOUT isn't really a file handle in your case. It's a tied object that presents the interface of a handle, but isn't actually. And layers (such as :encoding(UTF-8)) aren't supported by a tied handles.

So, rather than relying on an encoding layer, encode explicitly.

I could already hear the lynch mobs baying about the scandalous use of _utf8_off

And rightly so, since you're effectively encoding the the scalar using utf8 when is_utf8 is true, but you fail to do so when is_utf8 is false.

sub my_print($)
{
        my($string) = @_;
        my $is_utf8 = is_utf8(${$string});
        _utf8_off(${$string}) if($is_utf8);
        print ${$string};
        _utf8_on(${$string}) if($is_utf8);
}

my_print( \$string );
[download]

sub my_print($) {
   my $string_ref = shift;
   my $string = $$string_ref;
   utf8::encode( $string );
   print $string;
}

my_print( \$string );
[download]

Better yet,

sub my_print {
   my $s = join( $,, @_ ) . $\;
   utf8::encode( $s );
   print( $s );
}

my_print( $string );
[download]