I'm rather new to Drupal, and certainly not involved in development (yet?), but I have a suggestion to make about how translation / localization is done in Drupal. Currently, translation for each language is done in groups. These groups are usually very small (for example German translation project lists only 4 people, not all of them active), some are not even listed on drupal.org (hello, Japanese), and from what I can tell, they are almost all incomplete. If you're lucky, you get a 100% translation status on a fresh (core only) install for the more active translation projects. As soon as you start adding modules, however, this value drops rapidly down to 80%, 70%, 60% percent. There are so many modules for Drupal, and even for the existing ones, the original strings may change over time, so that already translated messages have to be re-translated. The way I see it, it's impossible for a small team of people to keep up.
Then there's the problem with the translation interface in Drupal itself; it is great that the system can give you a list of not yet translated strings, and allow you to translate them online. However, the problem here is that everyone does that for himself only. The translations do not get shared unless the site owner additionally makes an effort to join the appropriate translation group and / or forward his translations to the group in some way. But how many people actually do that? I know I didn't. When I installed Drupal for the first time, I discovered the translation interface, it took me a couple of minutes to add some missing ones, and that was it. I didn't even think about sharing this translation with others. This way it will never be of use to any other people.