How to use different domains for multilingual sites and keep users logged in? I have a site that is in French and English. I am able to successfully setup so that users can switch back and forth between the two domains to view either language, however I cannot seem to keep users logged in. When they are logged into the english domain and then switch to the french domain they are required to login again. However if they switch back to the english domain they are still logged in.

As an example we'll use www.english-domain.com as the base (default) domain and www.french-domain.com as the secondary domain

In settings.php I have modified the following, however it doesn't seem to be keeping them logged in. Am I missing something?

/**
 * Drupal automatically generates a unique session cookie name for each site
 * based on its full domain name. If you have multiple domains pointing at the
 * same Drupal site, you can either redirect them all to a single domain (see
 * comment in .htaccess), or uncomment the line below and specify their shared
 * base domain. Doing so assures that users remain logged in as they cross
 * between your various domains.
 */
$cookie_domain = 'english-domain.com';


Note: That I have also flushed both site and browser cache as well as deleted any cookies left on my machine.

Update:

Here are my language settings:
A cookie can only be read from the same domain that set it. This is a fundamental security feature in browsers to prevent other sites from potentially stealing login sessions, and there is nothing simple you can do about it.

With that said, the comment in the settings.php file seems to contradict my statement, and I'm honestly not really sure how to intrepret that. Perhaps it's only meant to be relevant to sub-domains, which are allowed to share cookies, but if so the comment should probably be re-phrased.

There are a number of ways to work around this, where the easiest is to use language prefix sub-domains instead of separate domains.

Baring that, I believe the "best" one is to use a Single sign-on system. There's a comparision of different SSO modules here. This could be a Drupal based solution, which is the way that is most likely to "nicely" integrate with your current Drupal sites, but that's not really necessary.

The Bakery module which is used by *.drupal.org itself is relevant to mention, as well as this related DA answer How drupal.org single sign on works

More info about cross-domain cookies in a Stack overflow question.