As my Google Summer of Code project went past its midterm evaluations, I’m happy to report that the core of the multilingualisation mechanism will be a part of the upcoming CiviCRM 2.1 release.
For CiviCRM 2.1, the multilingual support will be rather basic, but still quite usable. You’ll be able to add language switching to you CiviCRM install, and once you switch from one language to another, certain fields will be able to have different values.