add_action( 'woocommerce_process_product_meta', 'imc_sync_related_products_to_translations', 99 );
add_action( 'woocommerce_update_product', 'imc_sync_related_products_to_translations', 99 );
function imc_sync_related_products_to_translations( $product_id ) {
	if ( ! function_exists( 'icl_object_id' ) ) {
		return;
	}

	// Prevent infinite loops.
	static $syncing = array();
	if ( isset( $syncing[ $product_id ] ) ) {
		return;
	}
	$syncing[ $product_id ] = true;

	$meta_keys = array( '_crosssell_ids', '_upsell_ids' );

	foreach ( $meta_keys as $meta_key ) {
		$source_ids = get_post_meta( $product_id, $meta_key, true );
		if ( ! is_array( $source_ids ) || empty( $source_ids ) ) {
			continue;
		}

		$trid         = apply_filters( 'wpml_element_trid', null, $product_id, 'post_product' );
		$translations = apply_filters( 'wpml_get_element_translations', null, $trid, 'post_product' );

		if ( ! is_array( $translations ) ) {
			continue;
		}

		foreach ( $translations as $lang => $t ) {
			$target_pid = (int) $t->element_id;
			if ( $target_pid === $product_id ) {
				continue;
			}

			$translated_ids = array();
			foreach ( $source_ids as $src_id ) {
				$tr_id = apply_filters( 'wpml_object_id', $src_id, 'product', false, $lang );
				if ( $tr_id ) {
					$translated_ids[] = (int) $tr_id;
				}
			}

			if ( ! empty( $translated_ids ) ) {
				update_post_meta( $target_pid, $meta_key, $translated_ids );
			}
		}
	}
}{"id":4890,"count":0,"description":"","link":"https:\/\/electricsun.de\/es\/kategorie\/sunjoy-infrared-heating-panels-es\/","name":"Sunjoy infrared heating panels","slug":"sunjoy-infrared-heating-panels-es","taxonomy":"product_cat","parent":0,"meta":[],"menu_order":7,"_links":{"self":[{"href":"https:\/\/electricsun.de\/es\/wp-json\/wp\/v2\/product_cat\/4890","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/electricsun.de\/es\/wp-json\/wp\/v2\/product_cat"}],"about":[{"href":"https:\/\/electricsun.de\/es\/wp-json\/wp\/v2\/taxonomies\/product_cat"}],"wp:post_type":[{"href":"https:\/\/electricsun.de\/es\/wp-json\/wp\/v2\/product?product_cat=4890"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}