Extracted from http://drupal.org/node/1714474
You configure variables to be multilingual and domain-specific, separately. If you configure the same variables to be both "multilingual" and "domain-specific", then they will automatically show up as "multilingual domain variables". So, just go to settings for "multilingual variables" and select "sitename" and "frontpage", then go to settings for "domain variables" and do the same.
Once you have configured them, the realm selection widgets should automatically appear on the site-information form.