Fluent::detect_browser_locale PHP Method

    public static function detect_browser_locale($domain = null)
    {
        // Check for empty case
        if (empty($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
            return null;
        }
        // Given multiple canditates, narrow down the final result using the client's preferred languages
        $inputLocales = $_SERVER['HTTP_ACCEPT_LANGUAGE'];
        if (empty($inputLocales)) {
            return null;
        }
        // Generate mapping of priority => list of locales at this priority
        // break up string into pieces (languages and q factors)
        preg_match_all('/(?<code>[a-z]{1,8}(-[a-z]{1,8})?)\\s*(;\\s*q\\s*=\\s*(?<priority>1|0\\.[0-9]+))?/i', $inputLocales, $parsedLocales);
        $prioritisedLocales = array();
        if (count($parsedLocales['code'])) {
            // create a list like "en" => 0.8
            $parsedLocales = array_combine($parsedLocales['code'], $parsedLocales['priority']);
            // Generate nested list of priorities => [locales]
            foreach ($parsedLocales as $locale => $priority) {
                $priority = empty($priority) ? 1.0 : floatval($priority);
                if (empty($prioritisedLocales[$priority])) {
                    $prioritisedLocales[$priority] = array();
                }
                $prioritisedLocales[$priority][] = $locale;
            }
            // sort list based on value
            krsort($prioritisedLocales, SORT_NUMERIC);
        }
        // Check each requested locale against loaded locales
        foreach ($prioritisedLocales as $priority => $parsedLocales) {
            foreach ($parsedLocales as $browserLocale) {
                foreach (self::locales($domain) as $locale) {
                    if (stripos(preg_replace('/_/', '-', $locale), $browserLocale) === 0) {
                        return $locale;
                    }
                }
            }
        }
        return null;
    }

 /**
  * For incoming traffic to the site root, determine if they should be redirected to any locale.
  *
  * @return string|null The locale to redirect to, or null
  */
 protected function getRedirectLocale()
 {
     // Redirection interfere with flushing, so don't redirect
     if (isset($_GET['flush'])) {
         return null;
     }
     // Don't redirect if the user has clicked a link on the locale menu
     if ($this->knownReferrer()) {
         return null;
     }
     // Redirect if this user has previously viewed a page in any locale
     if (Fluent::config()->remember_locale && ($locale = Fluent::get_persist_locale())) {
         return $locale;
     }
     // Detect locale from browser Accept-Language header
     if (Fluent::config()->detect_locale && ($locale = Fluent::detect_browser_locale())) {
         return $locale;
     }
 }