#!/usr/bin/perl
    use strict;
    use warnings;

    my $utf8="\xe9";

    close (STDOUT);
    open( STDOUT, ">>:utf8", 'test.txt' ) or die $!;
    close STDERR;
    open( STDERR, ">>&STDOUT" ) or die $!;

    print        ("STDOUT: ",$utf8,"\n");
    print STDERR ("STDERR: ",$utf8,"\n");

    binmode (STDERR,':utf8');
    print STDERR ("STDERR with binmode: ",$utf8,"\n");
    
    
PRINTS:

    STDOUT: é
    STDERR: \xe9            (not literally - prints character \xe9, not UTF-8 encoded)
    STDERR with binmode: é