Although good for users, iCMS multilanguage system has some flaws that are damaging both the SEO effectiveness of any iCMS-powered multilingual site and the user experience.
Edit: You can find latest discussion on this subject on the ImpressCMS forum, here:
This hack changes iCMS core so it uses a different method for language selection when rendering, removing the need for cookies. The hack codifies the language right in the URL, so this:
...and so on.
The attached file includes detailed instructions for installation and a more technical explanation.