Issue #1392174 by Gábor Hojtsy, Garrett Albright, tstoeckler: Fixed install_find_translation_files() breaks if is passed.

core/includes/install.core.inc

@@ -1159,10 +1159,21 @@ function install_find_translations() {
 
 /**
  * Find installer translations either for a specific langcode or all languages.
+ *
+ * @param $langcode
+ *   (optional) The language code corresponding to the language for which we
+ *   want to find translation files. If omitted, information on all available
+ *   files will be returned.
+ *
+ * @return
+ *   An associative array of file information objects keyed by file URIs as
+ *   returned by file_scan_directory().
+ *
+ * @see file_scan_directory()
  */
 function install_find_translation_files($langcode = NULL) {
   $directory = variable_get('locale_translate_file_directory', conf_path() . '/files/translations');
-  $files = file_scan_directory($directory, '!install\.' . (!empty($langcode) ? '\.' . preg_quote($langcode, '!') : '[^\.]+') . '\.po$!', array('recurse' => FALSE));
+  $files = file_scan_directory($directory, '!install\.' . (!empty($langcode) ? preg_quote($langcode, '!') : '[^\.]+') . '\.po$!', array('recurse' => FALSE));
   return $files;
 }
 

core/modules/simpletest/simpletest.info

@@ -21,6 +21,7 @@ files[] = tests/filetransfer.test
 files[] = tests/form.test
 files[] = tests/graph.test
 files[] = tests/image.test
+files[] = tests/installer.test
 files[] = tests/lock.test
 files[] = tests/mail.test
 files[] = tests/menu.test