Hi Olivier,
Look at WPML documentation or ask their support how to set permission at WPML itself for other language for translators? May be you need to add a user to the translators list also.
As I mentioned earlier, if ‘Activate “Create” capability for posts/pages/custom post types’ option at URE Settings is turned ON, role requires “create_posts” capability in order to see “Posts->Add new” menu item. The same is true for other post types.
