use strict;
use warnings;

use Encode     qw( encode_utf8 );
use XML::Smart qw( );

my $text = chr(0xC9);
my $utf8 = encode_utf8($text);

my $doc = XML::Smart->new('<?xml version="1.0" encoding="UTF-8"?><root></root>');
$doc->{root}{node}{CONTENT} = $utf8;
$doc->save('a.xml', decode=>1);