Interface translation - Body, Title built-in interface
If having it only in Dutch is enough for you, you could change it to Dutch directly in the Edit content type form; go to Admin -> Content -> Content types, select edit for the one you want to change. You can set a title and body label in the "Submission form settings" fieldset.

There is a bug report open for this, see http://drupal.org/node/1016006.

I also found some reports that this should work now with multiple languages, with i18n: http://drupal.org/node/149349#comment-1135605.