Switch language key

zh_Hans -> zh-cn
zh_Hant -> zh-tw

data/web/inc/prerequisites.inc.php

@@ -194,7 +194,7 @@ require_once $_SERVER['DOCUMENT_ROOT'] . '/inc/sessions.inc.php';
 // Set language
 if (!isset($_SESSION['mailcow_locale']) && !isset($_COOKIE['mailcow_locale'])) {
   if ($DETECT_LANGUAGE && isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
-    $header_lang = strtolower(substr($_SERVER['HTTP_ACCEPT_LANGUAGE'], 0, 2));
+    $header_lang = strtolower($_SERVER['HTTP_ACCEPT_LANGUAGE']);
     if (array_key_exists($header_lang, $AVAILABLE_LANGUAGES)) {
       $_SESSION['mailcow_locale'] = $header_lang;
     }

data/web/inc/vars.inc.php

@@ -101,8 +101,8 @@ $AVAILABLE_LANGUAGES = array(
   'sk' => 'Slovenčina (Slovak)',
   'sv' => 'Svenska (Swedish)',
   'uk' => 'Українська (Ukrainian)',
-  'zh_Hans' => '简体中文 (Simplified Chinese)',
-  'zh_Hant' => '繁體中文 (Traditional Chinese)',
+  'zh-cn' => '简体中文 (Simplified Chinese)',
+  'zh-tw' => '繁體中文 (Traditional Chinese)',
 );
 
 // Change theme (default: lumen)