Ok, I quit with the design because I have first to build my site/store.
At this time, I have worked out the Multiple Stores en Locale/Language stuff. And yes I get it working.
The user have a global account and can visit every store or the global one with the prefered locale.
Users can change there preferred settings. I did not checked if it is working with products yet, but at this time I’m happy I get it working.
Let me know if something wrong by typing a reply in this topic because my site support in not set.
Thanks Magento, and community.
PS. Links are changed: