function filter_by_manufacture() {
$params = array(
    'name' => 'vyrobca',
    'show_option_all' => 'Vyberte výrobcu',
    'taxonomy'        => 'vyrobca',
    'show_count'         => 1,
    'value_field'      => 'slug'
);
if ( isset($_GET['vyrobca']) )
    $params['selected'] = $_GET['vyrobca'];

if ( get_post_type() == 'product' ) {
    wp_dropdown_categories( $params );
}
}
add_action('restrict_manage_posts', 'filter_by_manufacture');