wpml_sync_custom_field
Sync custom field value across all translations of a given post

WPML Version: 3.9.1

Synchronizes the value of a specified custom field across all translations of a given post. It only does it if the translation option for this custom field is set to Copy.

do_action( 'wpml_sync_custom_field', $post_id, $custom_field );

For this action hook, you only need to provide a post ID and the slug of the custom field you want to synchronize.

do_action( 'wpml_sync_custom_field', 1234, $event-date );