Fix formatDisplayName for language-specific directory names

- Add regex to handle nl.php-testen -> php-testen patterns
- Remove test directories that were cluttering navigation
- Clean up content directory to remove test files
- Language filtering now works correctly for both files and directories
- Navigation shows only relevant content for selected language

engine/core/class/CodePressCMS.php

@@ -541,6 +541,11 @@ class CodePressCMS {
             $filename = $matches[2];
         }
         
+        // Remove language prefixes from directory names (nl.php-testen -> php-testen)
+        if (preg_match('/^(nl|en)\.php-(.+)$/', $filename, $matches)) {
+            $filename = 'php-' . $matches[2];
+        }
+        
         // Handle special cases first
         if (strtolower($filename) === 'phpinfo') {
             return 'phpinfo';