setup multi language plugin

mkdocs.yml

 site_name: Chaos Communication Camp 2023
 site_description: Infos, news, links and more
-plugins: []
 site_dir: public
 use_directory_urls: false
 strict: true
 
+
+plugins:
+  - i18n:
+      default_language: en
+      languages:
+        de: Deutsch
+        en: English
+
 theme:
   name: null
   custom_dir: 'themes/c3mkdocs'
@@ -26,12 +33,3 @@ theme:
     search: 83   # s
 
 nav: []
-
-extra:
-  alternate:
-    - name: English
-      link: /en/ 
-      lang: en
-    - name: Deutsch
-      link: /de/
-      lang: de