Just to throw my part in here - I've just released a new version of the Url Master module which has a lot of specific Multi-Language Url enhancements. Essentially this is all about transforming the long example.com/pagename/tabid/xx/language/yy-ZZ/default.aspx Url of non-default language page and paring it back to zz.example.com/localized-page-name where
zz is a language specific subdomain [can also be example.zz or example.com/zz] and
localized-page-name is a Url for the page which is specific to that page.
Ranking well on language-specific search engines means allowing the search engine to detect a page as in a specific language, and not just, say, a bit of french on an otherwise english page. Separating the site content via domain name is a great way of doing that, and changing the Url to a keyword people are going to search for in that language is also very important. That's why I've gone down this route in order to give multi-language sites the best possible tools for search engine ranking - the fact that the Urls look better for visitors doesn't hurt either.
You can get more information on this at my blog post covering this:
DotNetNuke Multi Language Urls with Url Master 2.0
I haven't yet gone through all the 5.5 things - it's been a hard slog to get this far, but if it genuinely is page-as-language it's could mean a lot more work for me to support in the same way or to at least tweak it to look the way it needs to look for good SEO. That's OK though - all part of the challenge.
Chris - you cryptically mention there are some things you'd like done differently - feel free to contact me anytime with your thoughts: my 'door' is always open.