I needed to disable translations for a certain post type. After finally learning the existence of wpml-config.xml, I tried to copy it to the child theme and then switched the appropriate translation flag off. It didn't work.
Seems that polylang loads translations for both main and the child theme but loads the child xml first, which will then be overridden by the main theme.
I tried switching the order in includes/wpml-compat.php (init method, first 10 lines) and at least at a quick glance it seems to work just fine.
The same problem was reported in WPML in May: http://wpml.org/forums/topic/wpml-config-xml-problem-in-child-theme/