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.