Language_List and default language as selected option on Drupal 6x

Just add global $language to function locale_form_alter and change line 278 on locale module:

change:

'#default_value' => (isset($form['#node']->language) ? $form['#node']->language : ''),

with:

'#default_value' => (!empty($form['#node']->language) ? $form['#node']->language : $language->language),