wcml_product_content_fields

/*
 * Add this code to the functions.php file of your theme.
 */
add_filter( 'wcml_product_content_fields', 'add_custom_fields_wcml_editor', 10, 2 );

function add_custom_fields_wcml_editor ( $fields, $product_id ) {

	// Add the 'new_button_label' field to WCML Translation Editor 
	$fields[] = 'new_button_label'; 
	return $fields;
}