Redirect users to context based on browser language setting

RewriteEngine On
RewriteBase /

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(en|fr|de|it)/favicon.png$ favicon.png [L,QSA]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(en|fr|de|it)/assets(.*)$ assets$2 [L,QSA]
RewriteRule ^en/iphone/info6html en/iphone/info6.html [L]
RewriteRule ^de/iphone/info.html3 de/iphone/info3.html [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(en|fr|de|it)?(\/)?(.*)$ index.php?c=$1&q=$3 [L,QSA]

<?php
//make sure the plugin does not run on the mgr context (the manager)
  if ( $modx->context->get( 'key' ) != 'mgr') {
    /**
     * grab the current context from the request "c" parameter (or context_param_alias from system settings)
     * the alternative .htaccess friendly URL rewrite rule must be activated
     */
    $cntxt_param = $modx->getOption('context_param_alias', null, 'c');
    if ( isset( $_REQUEST[$cntxt_param] ) && $_REQUEST[$cntxt_param] != '' ) {
      switch ( $_REQUEST[$cntxt_param] ) {
          
        case 'en':
          //switch the context
          $modx->switchContext('web');
          //set the cultureKey
          $modx->setOption('cultureKey', 'en');
          break;
          
        case 'fr':
          $modx->switchContext('fr');
          $modx->setOption('cultureKey', 'fr');
          break;
          
       case 'de':
          $modx->switchContext('de');
          $modx->setOption('cultureKey', 'de');
          break;

       case 'it':
          $modx->switchContext('it');
          $modx->setOption('cultureKey', 'it');
          break;
          
        default:
          // Set the default language/context here
          break;
      }
    }
  }

$_SERVER['HTTP_ACCEPT_LANGUAGE']

$_SERVER['HTTP_ACCEPT_LANGUAGE'];

<?php
//make sure the plugin does not run on the mgr context (the manager)
  if ( $modx->context->get( 'key' ) != 'mgr') {
  
	  switch ( $_SERVER['HTTP_ACCEPT_LANGUAGE'] ) {
	       
	      case 'fr':
	      $modx->switchContext('fr');
	      $modx->setOption('cultureKey', 'fr');
	      break;
	       
	   case 'de':
	      $modx->switchContext('de');
	      $modx->setOption('cultureKey', 'de');
	      break;
	
	   case 'it':
	      $modx->switchContext('it');
	      $modx->setOption('cultureKey', 'it');
	      break;
	       
	    default:
	      $modx->switchContext('web');
	      //set the cultureKey
	      $modx->setOption('cultureKey', 'en');
	      break;
	  }
  }

$cntxt_param = $modx->getOption('context_param_alias', null, 'c');
    if ( isset( $_REQUEST[$cntxt_param] ) && $_REQUEST[$cntxt_param] != '' ) {
      switch ( $_REQUEST[$cntxt_param] ) {

<?php
// get lang from URI
$uri= ($_SERVER['REQUEST_URI']);
$langFromUri = substr($uri, 1, 2);
switch ($langFromUri) {
  case 'zh':
    //set the cultureKey
    $modx->setOption('cultureKey', 'zh');
    break;
  case 'en':
    //set the cultureKey
    $modx->setOption('cultureKey', 'en');
    break;
  case 'de':
    //set the cultureKey
    $modx->setOption('cultureKey', 'de');
    break;
  default:
    // detect language and call corresponding start-page
    $langPrefered = substr($_SERVER['HTTP_ACCEPT_LANGUAGE'], 0, 2);
    switch ($langPrefered) {
      case 'en':
        $targetId = 2;
        break;
      case 'zh':
        $targetId = 3;
        break;
      default:
        $targetId = 1;
        $langPrefered="de";
        break;
    }
    //set the cultureKey
    $modx->setOption('cultureKey', $langPrefered);
    //call correct start page
    $url=$modx->makeUrl($targetId);
    $modx->sendRedirect($url);	

  break;
}

return;