private function loadLang($lang) {
        $locale = preg_replace_callback('/\b([a-z]{2})[-_](?:([a-z]{4})[-_])?([a-z]{2})\b/', function ($matches) {
            return $matches[1].'_'.(!empty($matches[2]) ? ucfirst($matches[2]).'_' : '').strtoupper($matches[3]);
        }, strtolower($lang));

        if (file_exists($filename = __DIR__.'/Lang/'.$locale.'.php')) {
            $this->lang = $locale;

            $this->number_word = include __DIR__.'/Lang/'.$locale.'.php';
            $this->currency = $this->number_word['currency'];

            return true;
        }
        throw new InvalidArgumentException('Unknown language ('.$lang.')');
    }