bpo-36425: Add Simplified Chinese to the language switcher (GH-12537)

(cherry picked from commit 45a5fdb91cee665161a8b1980bb4e6ccb999f58f)

Co-authored-by: zhsj <zsj950618@gmail.com>
diff --git a/Doc/tools/static/switchers.js b/Doc/tools/static/switchers.js
index 20dad93..346b314 100644
--- a/Doc/tools/static/switchers.js
+++ b/Doc/tools/static/switchers.js
@@ -22,6 +22,7 @@
       'fr': 'French',
       'ja': 'Japanese',
       'ko': 'Korean',
+      'zh-cn': 'Simplified Chinese',
   };
 
   function build_version_select(current_version, current_release) {