protected function mergeTranslation($merge_file, $langcode = null)
    {
        $common_file = $this->getCommonFile($langcode);
        $merge_translations = $this->loadTranslation($merge_file);
        $common_translations = $this->loadTranslation($common_file);

        if (!empty($merge_translations)) {
            foreach ($merge_translations as $source => $translation) {
                if (!isset($common_translations[$source])) {
                    array_unshift($translation, $source);
                    gplcart_file_csv($common_file, $translation);
                }
            }
        }
    }