If you are using WPML with WooCommerce Multilingual, WooCommerce & Composite Products and get an error when attempting to add a Composite to your cart, this snippet might fix the issue.

woocommerce-composites-wpml-fix.php

<?php
/**
 * Plugin Name: WooCommerce Composite Products - WPML Cart Error Fix
 * Plugin URI: http://www.woothemes.com/products/composite-products/
 * Description: If you are using WPML with WooCommerce Multilingual, WooCommerce & Composite Products and get an error when attempting to add a Composite to your cart, this snippet might fix the issue.
 * Version: 1.1
 * Author: Manos Psychogyiopoulos
 * Author URI: http://www.somewherewarm.net/
 *
 * Requires at least: 3.8
 * Tested up to: 4.0
 *
 * Copyright: © 2014 Manos Psychogyiopoulos ([email protected]).
 * License: GNU General Public License v3.0
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 */

// To use this snippet, download this file into your plugins directory and activate it, or copy the code under this line into the functions.php file of your (child) theme.

add_filter( 'wcml_cart_contents', 'wpml_composites_compat', 11, 4 );
add_filter( 'wcml_exception_duplicate_products_in_cart', 'wpml_composites_dupicate_exception', 10, 2 );
add_filter( 'woocommerce_composite_component_options_query_args', 'wpml_composites_transients_cache_per_language', 10, 3 );

function wpml_composites_compat( $new_cart_data, $cart_contents, $key, $new_key ) {

	global $sitepress;

	if ( isset( $cart_contents[ $key ][ 'composite_children' ] ) || isset( $cart_contents[ $key ][ 'composite_parent' ] ) ) {

		$buff = $new_cart_data[ $new_key ];

		unset( $new_cart_data[ $new_key ] );

		$new_cart_data[ $key ] = $buff;
	}

	return $new_cart_data;
}

function wpml_composites_dupicate_exception( $exclude, $cart_item ) {

	if ( isset( $cart_item[ 'composite_parent' ] ) || isset( $cart_item[ 'composite_children' ] ) ) {
		$exclude = true;
	}

	return $exclude;
}

function wpml_composites_transients_cache_per_language( $args, $query_args, $component_data ) {

	global $sitepress;

	$args[ 'wpml_lang' ] = $sitepress->get_current_language();

	return $args;
}