Index: branches/RC/core/units/languages/languages_event_handler.php
===================================================================
diff -u -r8929 -r9363
--- branches/RC/core/units/languages/languages_event_handler.php	(.../languages_event_handler.php)	(revision 8929)
+++ branches/RC/core/units/languages/languages_event_handler.php	(.../languages_event_handler.php)	(revision 9363)
@@ -55,6 +55,8 @@
 			if ($ids) {
 				$id = array_shift($ids);
 				$object =& $event->getObject( Array('skip_autoload' => true) );
+				/* @var $object LanguagesItem */
+
 				$object->Load($id);
 				$object->setPrimary();
 			}
@@ -68,16 +70,21 @@
 		function OnUpdatePrimary(&$event)
 		{
 			$object =& $event->getObject( Array('skip_autoload' => true) );
+			/* @var $object LanguagesItem */
+
 			$object->SwitchToLive();
 
 			// set primary for each languages, that have this checkbox checked
 			$ids = explode(',', $event->MasterEvent->getEventParam('ids'));
 			foreach ($ids as $id) {
 				$object->Load($id);
 				if ($object->GetDBField('PrimaryLang')) {
-					$object->setPrimary();
+					$object->setPrimary(true, false);
 				}
 
+				if ($object->GetDBField('AdminInterfaceLang')) {
+					$object->setPrimary(true, true);
+				}
 			}
 
 			// if no primary language left, then set primary last language (not to load again) from edited list
@@ -87,8 +94,17 @@
 			$primary_language = $this->Conn->GetOne($sql);
 
 			if (!$primary_language) {
-				$object->setPrimary(false);
+				$object->setPrimary(false, false); // set primary language
 			}
+
+			$sql = 'SELECT '.$object->IDField.'
+					FROM '.$object->TableName.'
+					WHERE AdminInterfaceLang = 1';
+			$primary_language = $this->Conn->GetOne($sql);
+
+			if (!$primary_language) {
+				$object->setPrimary(false, true); // set admin interface language
+			}
 		}
 
 
@@ -453,7 +469,7 @@
 			$object =& $event->getObject(array('skip_autload' => true));
 			$object->Load($del_id);
 
-			if ($object->GetDBField('PrimaryLang') || $del_id == $this->Application->GetVar('m_lang')) {
+			if ($object->GetDBField('PrimaryLang') || $object->GetDBField('AdminInterfaceLang') || $del_id == $this->Application->GetVar('m_lang')) {
 				$event->status = erFAIL;
 			}
 		}