The current configuration includes many modules, a.o. I18n, Content Access, Views and CCK. With these I’m able to define roles, grant restricted access to nodes based on roles and keep the site bi-lingual (Dutch and English, with the largest part of the content in Dutch). This works fairly well.
On the other hand, assignment has to be done by hand. I haven’t figured out yet how to grant permission to another user to just restrict content to one particular role and I guess I need to build a custom View to see which nodes are restricted, i.e. build my own administrative views. As said before, it’s easy to make a mistake and grant the wrong role to a user. I also haven’t looked into the Drupal forum to see if role-based restrictions are possible. Just had a quick look: the Forum Access module and Content Access are recommended for restricted forums (the first one also allows the setup of moderators).