Official: WordPress default theme translation is forbidden
Whether WordPress default theme can be translated, this issue keeps popping up once in a while. While many translators want to make it usable for most people in the world, Matt Mullenweg resisted this idea with plain blank refusal. Well, at least there is a final answer now.
First the (old) news: the default theme won’t be i18n-ed. The reason in short: for the sake of simplicity.
I beg you, let’s not make a flame war on that, I am almost sure this policy won’t change, so we’d better focus on making our life easier, instead of losing precious time for pointless discussions. Thank you!
Probably due to Matt’s ever-increasing power. I have already given up long time ago, seeing that it just wastes my time. Am I wise? Probably other translators have also realised this dead-end — wp-polyglot list is usually as quiet as a mouse. Anyway, case closed.

Welcome to the club.
Gotta admit though that themes not supporting translation is a big issue with wordpress. Many many themes don’t have this built in and it’s really a shame, especially with Wordpress Multiuser now available. (For reference, end users can’t edit the themes in wpmu as they don’t have file level access and the themes are shared among the blogs.)