Add multilingual support (DE default, EN under /en/)

.htaccess

@@ -8,7 +8,18 @@ RewriteCond %{THE_REQUEST} \s/+index\.php[\s?] [NC]
 RewriteCond %{QUERY_STRING} ^$
 RewriteRule ^index\.php$ / [R=301,L]
 
-# Clean URL routing for .html pages
+# Redirect /de/... to canonical root /... (German is the default language)
+RewriteRule ^de/?$ / [R=301,L]
+RewriteRule ^de/main\.html$ / [R=301,L]
+RewriteRule ^de/([0-9a-zA-Z\-]+)\.html$ /$1.html [R=301,L]
+
+# English subpath routing (/en/ and /en/<page>.html)
+RewriteRule ^en/main\.html$ /en/ [R=301,L]
+RewriteRule ^en/?$ index.php?lang=en&action=main [QSA,L]
+RewriteCond %{REQUEST_FILENAME} !-f
+RewriteRule ^en/([0-9a-zA-Z\-]+)\.html$ index.php?lang=en&action=$1 [QSA,L]
+
+# Clean URL routing for .html pages (German default)
 RewriteCond %{REQUEST_FILENAME} !-f
 RewriteCond %{QUERY_STRING} ([a-zA-Z0-9-_.=&+%]*)
 RewriteRule ^([0-9a-zA-Z\-]+).html$ index.php?action=$1&%1 [L]