How do I add a Site Information variable and make it multilingual?
So I managed to solve this after searching through Drupal's code and the Variable module. Turns out if you add a call to hook_variable_info, it will add it into the multilingual variables list, and then if you check that off, it makes it translatable like the rest of the Site Information.

/**
 * Implements hook_variable_info().
 */
function omm_variable_info($options) {
  // Site configuration, site information
  $variables['site_pretitle'] = array(
    'type' =&gt; 'text',
    'title' =&gt; t('Site Pre-Title', array(), $options),
    'default' =&gt; '',
    'description' =&gt; t("This will appear above the website name on all pages.", array(), $options),
    'group' =&gt; 'site_information',
  );

  return $variables;
}


After adding this, go to admin/config/regional/i18n/variable and click on the Site information group.  Click the checkmark beside your variable (site_pretitle for mine), and hit Save configuration. Once that's done, return to the Site Information area (admin/config/system/site-information) and you should see it appear and say This is a multilingual variable. in bold.