Want to rename contact form fields name
Use hook_form_FORM_ID_alter() as shown below:

/**
 * Implements hook_form_FORM_ID_alter().
 */
function MODULENAME_form_contact_site_form_alter(&amp;$form, &amp;$form_state) {
    $form['subject']['#title'] = t('New Title');
}


Update #1

For Page Title use drupal_set_title() as shown below:

drupal_set_title('kontakt'); // Add this line in above function MODULENAME_form_contact_site_form_alter