Work Around for Multi Language for the sake of SEO..question.

[thethreedegrees]

Hi,
been reading through the various posts regarding SEO for multi-lingual shops. Found a few links which offer different suggestions.
However I would like to suggest and hopefully the PS experts can let me know if they think my work-around will work before I dive in and try it.
The bottom line for me(as I am sure is for so many others) is to get listed on various search engines in native languages and these include French,Spanish and Greek.

Here is my suggestion:
My existing domain is mydomain.com
I create sub-domains such as fr.mydomain.com es.mydomain.com,gr.mydomain.com and within them install a version of prestashop using the default language such as French for fr.mydonain.com, Spanish for es.mydonain.com etc. Use the native language for each of my product categories etc. and the search engines should pick them up no problem.

Now here is the tricky part.
The only thing I want to do is when a customer is going to BUY a product in other words when he clicks on my-account or authentication.php from the sub-domain directory he gets REDIRECTED to the main site(TLD) which is mydomain.com and submits his order on the original backend DB. Because as far as I can tell the cookie can now be used in different sub-domains of a site according to the BO tab "tools".
Do you think it could work?

Update: Yes the problem is I cannot pass the re-directed URL to the original shop directory(TLD) because of the cookie.
Anyone know how we can make the cookie work domain wide?