You could also write everything in one blog and have a tag for each language. Then you can point readers to the URL with one language included. For example, all my German posts: http://thomas11.wordpress.com/tag/de/. Works with RSS, too. Only the UI will be in one language only, people would have to live with that.
Using Firefox with a “Translator” extension could help your surfers. I have a little double flag icon at the bottom of my screen, and a right click and “translate …. to ……” does a computer translation and shows the new results in a new tab / window.
It may not be THE solution you’re looking for, but it is A solution.
This feature is already available in Worpress CMS… I wonder why it is not made available for bilingual bloggers using the hosted version of WordPress… this feature will be beneficial not only for bloggers, but also will bring much more hits to WordPress itself.