code: public static function getMessageText( $id, $key ) {
  		$string  = 'mw-ext-' . $id . '-' . $key;
  		$message = wfMessage( $string )->inContentLanguage();
  		$out     = $message->text();
  
  		return $out;
  	}
docs: Wiki Framework: Message.
  
  @param $id
  @param $key
  
  @return string