WP being singlelingual is a major drawback on a system that I absolutely love in most other respects.
Having a translation plugin does not mean you can have a truly multilingual site. Sure it handles posts, pages and themes but as long as there is no language selector in the core the system is seriously crippled. My main grief is with the wp-login.php only observing the one globally set language.
Now that the premier choice – WPML – got greedy and went commercial it would be high time for the WP community to really address this issue.