I have installed Dojo locally and bootstrapped it in the following way:

Zend_Dojo::enableView($view);
$view->dojo()->setDjConfig(array(
                'parseOnLoad' => true,
                'locale' => $language       // Set language
             ))
             ->setLocalPath($fc->getBaseUrl() . '/js/dojo/dojo.js')
             ->addStyleSheetModule('dijit.themes.tundra')
     ->disable();                   // Enable only when necessary

If I try to change DateTextBox locale from default ($language in bootstrap) to something else, for example to en, by using setLocale(), nothing happens.

$this->addElement('DateTextBox', 'calendar', array(
    'required'     => true,
    'label'        => 'calendar',
    'formatLength' => 'short',
    'locale'       => 'en',
));