Windows: reorganize localized documentation, each in a dedicated folder. Adapt installers and documentation URL logic.

Now we have 3 folders under html directory：en, ru, zh-cn. Similar separation exist in online version:
https://veracrypt.fr/en
https://veracrypt.fr/ru
https://veracrypt.fr/zh-cn

doc/html/zh-cn/donation.js

@@ -0,0 +1,9 @@
+document.addEventListener('DOMContentLoaded', function() {  
+    document.getElementById('currency-form').addEventListener('submit', function(e) {  
+        e.preventDefault();  
+        const select = this.querySelector('select');  
+        if (select.value) {  
+            window.open(select.value, '_blank');  
+        }  
+    });  
+});