Hello,

In /mod/messages/actions/delete.php  you have to change (!array($message_id_array)) by (!is_array($message_id_array)) in line 20. Without this you can't delete messages with the cross.

In /mod/messages/view/default/messages/messages.php you have to change line 131 by
    <p><label><?php echo elgg_echo("messages:title"); ?>: <br /><input type='text' name='title' class="input-text" value="RE: <?php echo str_replace(chr(34),chr(38).chr(113).chr(117).chr(111).chr(116).chr(59),$vars['entity']->title); ?>" /></label></p> If you want to use ' and " in your object. Without this you will have trouble when you answer to a message with theses caracters in object (object will be cut).

If you want to add the previous message in your answer, replace the code between <div id="message_reply_editor"> (line 133) and <.div> by this code :
    <?php
            if ($vars['entity']->description != '') {
              $message_precedent_clair = utf8_decode($vars['entity']->description);
              $message_precedent_clair = '> '.str_replace("\n","\n> ",html_entity_decode($message_precedent_clair))."\n\n";
              $message_precedent = utf8_encode($message_precedent_clair);
            } else {
              $message_precedent = utf8_encode(">\n\n");
            }
        echo elgg_view("input/longtext", array(
         "internalname" => "message",
         "value" => $message_precedent,
             ));
   
          ?>

I wasn't able to register myself to the trac so I post here this code.

Have a nice day !

Christophe