To reproduce, go to ACP > System > Manage report/denial reasons. Add a custom denial reason (e.g., BECAUSE -> "Because I said so"). Now disapprove a post. The notification message shown should include "Because I said so". Instead it shows a simple "." (see attached screenshot).

I believe this is the fix:

OPEN: mcp_queue.php
FIND: $post_data['disapprove_reason'] = "";
REPLACE WITH: $post_data['disapprove_reason'] = $disapprove_reason;

It appears this occurs because the custom report/denial isn't localized. Note: Reason is correctly logged in the ACP > Maintenance > Moderator log.