use strict;
use warnings;

use open ':std', ':locale';
use charnames ':full';

use Encode qw( encode );
use WWW::Mechanize qw( );

# Avoiding script encoding issues.
my $val = "Ch\N{LATIN SMALL LETTER A WITH CIRCUMFLEX}teau";

my $mech = WWW::Mechanize->new( autocheck => 1 );
$mech->get('http://www.server.com/zzz.cgi');

$mech->field('key', $val);
$mech->submit();

#print($mech->value('key'), "\n");
use Devel::Peek qw( Dump );
Dump($mech->value('key'));