How to override form id of Webform?
You can simply do following way, using hook_form_alter, paste following code in your template.php file, save and clear cache. Change the THEME with your themeName in code or if you are doing with costume module then with module name.

In your case the code will be,

function THEME_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id == 'webform_141') {
    $form['#id'] = 'webform_en';
  }
}