Method detectLanguage

/**
 * Tries to detect the language.
 *
 * @return  string  locale or null if not found
 *
 * @since   1.5
 */
public static function detectLanguage()
{
    if (isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
        $browserLangs = explode(',', $_SERVER['HTTP_ACCEPT_LANGUAGE']);
        $systemLangs = self::getLanguages();
        foreach ($browserLangs as $browserLang) {
            // Slice out the part before ; on first step, the part before - on second, place into array
            $browserLang = substr($browserLang, 0, strcspn($browserLang, ';'));
            $primary_browserLang = substr($browserLang, 0, 2);
            foreach ($systemLangs as $systemLang) {
                // Take off 3 letters iso code languages as they can't match browsers' languages and default them to en
                $Jinstall_lang = $systemLang->lang_code;
                if (\strlen($Jinstall_lang) < 6) {
                    if (strtolower($browserLang) == strtolower(substr($systemLang->lang_code, 0, \strlen($browserLang)))) {
                        return $systemLang->lang_code;
                    } elseif ($primary_browserLang == substr($systemLang->lang_code, 0, 2)) {
                        $primaryDetectedLang = $systemLang->lang_code;
                    }
                }
            }
            if (isset($primaryDetectedLang)) {
                return $primaryDetectedLang;
            }
        }
    }
}