Index: user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.module,v
retrieving revision 1.1062
diff -u -r1.1062 user.module
--- modules/user/user.module	10 Oct 2009 21:39:03 -0000	1.1062
+++ modules/user/user.module	11 Oct 2009 11:23:34 -0000
@@ -3136,6 +3136,12 @@
   $form_state['values']['pass'] = $pass;
   $form_state['values']['init'] = $form_state['values']['mail'];
 
+  // If no language was submitted use the currently active language so we can
+  // translate any user related message properly.
+  if (empty($form_state['values']['language'])) {
+    $form_state['values']['language'] = $GLOBALS['language']->language;
+  }
+
   $account = $form['#user'];
   $account = user_save($account, $form_state['values']);
   // Terminate if an error occurred during user_save().
Index: user.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.test,v
retrieving revision 1.63
diff -u -r1.63 user.test
--- modules/user/user.test	10 Oct 2009 16:48:39 -0000	1.63
+++ modules/user/user.test	11 Oct 2009 11:23:36 -0000
@@ -123,7 +123,7 @@
     $this->assertTrue(($new_user->created > REQUEST_TIME - 20 ), t('Correct creation time.'));
     $this->assertEqual($new_user->status, variable_get('user_register', 1) == 1 ? 1 : 0, t('Correct status field.'));
     $this->assertEqual($new_user->timezone, variable_get('date_default_timezone'), t('Correct time zone field.'));
-    $this->assertEqual($new_user->language, '', t('Correct language field.'));
+    $this->assertEqual($new_user->language, $GLOBALS['language']->language, t('Correct language field.'));
     $this->assertEqual($new_user->picture, '', t('Correct picture field.'));
     $this->assertEqual($new_user->init, $mail, t('Correct init field.'));
   }