Non-UTF characters break RSS feed

copy this code in a php file, copy this file in your plugins-folder and after this activate it on the backend of WordPress. I hope this helps, but i dont test it, write it on scratch.

<?php
/**
 * Plugin Name: Non-UTF characters in RSS feed
 * Plugin URI:  http://wordpress.stackexchange.com/questions/37845/non-utf-characters-break-rss-feed/
 * Description: Filter content for unicode characters
 * Version:  1.0.0
 * Author:      Frank Bültge
 * Author URI:  http://bueltge.de
 * License:     GPLv3
 */

// This file is not called from WordPress. We don't like that.
! defined( 'ABSPATH' ) and exit;

foreach ( array( 'the_content_rss', 'the_excerpt_rss', 'the_title_rss', 'comment_text_rss' ) as $filter )
    remove_filter( $filter, 'filter_non_utf8_chars', 0 );

function filter_non_utf8_chars( $content ) {

    return htmlentities2( $content );
}
?>