unique formatting for translation files (Zend2). This way I manage exception Firefox.
$language = \Locale::acceptFromHttp(array_key_exists('HTTP_ACCEPT_LANGUAGE',$_SERVER) ? $_SERVER['HTTP_ACCEPT_LANGUAGE'] : 'it_IT');
if(strpos($language,'_') === false){
$language = $language.'_'.strtoupper($language);
}