Fix the loop to search al the available languages, not only the las element.

lib/l10n.php

@@ -298,13 +298,13 @@ class OC_L10N{
 				if( ($key = array_search($temp[0], $available)) !== false) {
 					return $available[$key];
 				}
-			}
 				foreach($available as $l) {
 					if ( $temp[0] == substr($l,0,2) ) {
 						return $l;
 					}
 				}
 			}
+		}
 
 		// Last try: English
 		return 'en';