Sites migrated from Zope 2.8 don't have a configured component manager (a.k.a.
SiteManager) and because of that, and its consequent lack of registration of
the Localizer Message Catalogs as ITranslationDomain utilities, they don't
perform translation correctly.

Here we add a no-additional-cost migration by overriding the
ObjectManager.getSiteManager() method, and automatically configuring the
component manager, including translation domains.