Allow locale to be added to permalink URL structure

The WordPress integration of gettext makes internationalization/localization very simple. It is easy to setup locale switching with .mo files. One thing I cannot do though is have SEO-friendly URLs for different locales. It would be nice if the permalink options allowed for a structure that included the locale in all WordPress URLs. Something like:

/%locale%/%year%/%monthnum%/%day%/%postname%/
/en-US/2010/02/20/my-blog-post/

But for every WordPress URL too; not just posts. Then I could use a rewrite rule to retrieve the locale, or that support could even be built into WordPress.