We've got the comment merging working with the latest WordPress and WPML for all post types. Caveat: I have a very strong feeling that this patch won't help if you want to use translated comments, but I may be wrong about that (so test if you want to use this feature and don't just trust me).
Replace the merge_comments function in the latest version of the plugin with this:
function merge_comments($comments, $post_ID) {
global $sitepress;
remove_filter( 'comments_clauses', array( $sitepress, 'comments_clauses' ) );
// get all the languages for which this post exists
$languages = icl_get_languages('skip_missing=1');
$post = get_post( $post_ID );
$type = $post->post_type;
foreach($languages as $code => $l) {
// in $comments are already the comments from the current language
if(!$l['active']) {
$otherID = icl_object_id($post_ID, $type, false, $l['language_code']);
$othercomments = get_comments( array('post_id' => $otherID, 'status' => 'approve', 'order' => 'ASC') );
$comments = array_merge($comments, $othercomments);
}
}
if ($languages) {
// if we merged some comments in we need to reestablish an order
usort($comments, 'sort_merged_comments');
}
//
add_filter( 'comments_clauses', array( $sitepress, 'comments_clauses' ) );
return $comments;
}
If you want a diff, you can find one here: http://pastebin.com/f1VFG4t2