Index: branches/RC/core/install/upgrades.php
===================================================================
diff -u -r9127 -r9363
--- branches/RC/core/install/upgrades.php	(.../upgrades.php)	(revision 9127)
+++ branches/RC/core/install/upgrades.php	(.../upgrades.php)	(revision 9363)
@@ -157,6 +157,37 @@
 			}
 		}
 
+		/**
+		 * Makes admin primary language same as front-end
+		 *
+		 * @param string $mode when called mode {before, after)
+		 */
+		function Upgrade_4_2_1($mode)
+		{
+			if ($mode == 'after') {
+				$id_field = $this->Application->getUnitOption('lang', 'IDField');
+				$table_name = $this->Application->getUnitOption('lang', 'TableName');
+
+				$sql = 'SELECT '.$id_field.'
+						FROM '.$table_name.'
+						WHERE PrimaryLang = 1 AND Enabled = 1';
+				$language_id = $this->Conn->GetOne($sql);
+
+				if ($language_id) {
+					// reset admin language
+					$sql = 'UPDATE '.$table_name.'
+							SET AdminInterfaceLang = 0';
+					$this->Conn->Query($sql);
+
+					// set admin language to front-end
+					$sql = 'UPDATE '.$table_name.'
+							SET AdminInterfaceLang = 1
+							WHERE '.$id_field.' = '.$language_id;
+					$this->Conn->Query($sql);
+				}
+			}
+		}
+
 	}
 
 ?>
\ No newline at end of file