I have a Drupal site where the "Multilingual support" options don't show up when editing a content type. I've checked to make sure that the line that adds the options executes (you can see it at http://api.drupal.org/api/function/translation%5Fform%5Falter/6 ). I also have another copy of the same code on a different server which has the same problem (one server is Apache on Windows the other is Apache on Linux).
I have another, similar site that doesn't have the problem.
The option group shows up, everything but the buttons are there in the source delivered to the browser. I've turned off all custom and most all contrib modules and I still get the same problem.