Google's Jens O. Meiert and Tony Ruscoe posted on the Google Webmaster Blog 6 quick tips for international web sites.
The 6 tips in short are:
1. Make pages I18N-ready in the markup, not the style sheets
2. Use one style sheet for all locales
3. Use the [dir='rtl'] attribute selector
4. Use the :lang() pseudo class
5. Mirror left- and right-related values
6. Keep an eye on the details
Now, a WebmasterWorld thread asked why is Google saying to use the language attribute when it doesn't seem to work. One webmaster said, "Google ignores code level language informations," so why are they recommending it? Do they really ignore that information? I didn't think they do.
In any event, feel free to join the discussion on these tips in the forums.