Special:ContentTranslation is a tool to create pages. It should be impossible to even start using if the user doesn't have a permission to create pages.
Creating pages is allowed by default to all users, including anons, but some wikis customize it. In particular:
- Blocked users can't create pages.
- Some Wikimedia wikis don't allow anons to create pages. See http://noc.wikimedia.org/conf/highlight.php?file=InitialiseSettings.php and search for createpage .
- The Tamil Wikipedia has a group for users that can't create new pages: "nocreate".
All of the above must not be allowed to user Special:CX.