I am currently making a bilingual website and I'd like to get nice SEO results of course.

Here's my idea:

The internal links would be composed of the "www" subdomain so that people can share links regardless of their language. Anyway, their language is determined by the HTTP_ACCEPT_LANGUAGE PHP variable.

So, they would see http:// www.site.com/mydocument/123 in their adress bar and never see any links like "http:// fr.site.com/mydocument/123" or "http://en.site.com/mydocument/123"

The user can always switch the page's language thanks to links in the footer.
The switching language link would be : http:// fr.site.com/mydocument/123 , and clicking on it would change his language session and redirects the user to http:// www.site.com/mydocument/123

In case of a crawling bot:

I read that if the HTTP_USER_LANGUAGE variable was missing then it's a crawling bot.

So, in that case, we set the defaut language as English. Each page, as I mentionned earlier, has a link for another language:
On the page: http:// www.site.com/document/1323, the link http:// fr.site.com/document/1323 can be seen by the bot and be crawled.

• What do you think about this practise ?
• Would I get good SEO results for each language ?