If widget Language switcher doesn’t work with WPML?

Then search for:

// Is the instance a nav menu and are descriptions enabled?
if ( isset( $new_instance['nav_menu'] ) && !empty( $new_instance['split-nav-menu'] ) ) {
	$new_instance['split-nav-menu'] = 1;
}

return $new_instance;

and then replace it by

// Is the instance a nav menu and are descriptions enabled?
if ( isset( $new_instance['nav_menu'] ) && !empty( $new_instance['split-nav-menu'] ) ) {
	$instance['split-nav-menu'] = 1;
}

return $instance;

That’s all.