Actually I cannot provide the full detailed answer but: At least you need to create a Router to match the new translation strings.
Matthias created an extension "Magento Language Routes" for this a frew days ago:
Features
Translate all URLs for each store (e.g. /customer/account/create -> /kunde/konto/erstellen)
Easy translation without development skills by using the backend Translate third party extensions out of the box
Ability to translate URLs to CMS pages, too
Extension uses the Magento Cache to avoid performance issues
Manage permissions for translations by roles
Old URLs are still working (even if they translated)
https://github.com/klein0r/magento-language-routes
I know that this is not a very detailed technical answer, but that might also be a bit too much here i guess.
