Zend Form can't validate float number

I have this form element:

$this->addElement('text', 'prezzo', array(
        'label' => 'Prezzo (*)',
        'filter' => '',
        'description' => 'Il prezzo non è comprensivo di sconto, ma se previsto verrà calcolato',
        'required' => true,
        'validators' => array('Float'),
        'placeholder' => 'Prezzo Pneumatico',
        'class' => 'form-control'
    ));

if i put in input a number like this 24.50 I get error on validation while if i put a number like this 24,50 I don't get any error.

I think the problem is with Zend_Locale in my Bootstrap.php where i set this value:

protected function _initLocale() {
    $locale = new Zend_Locale ( 'it' );
    Zend_Registry::set ( 'locale', $locale );
}

Probably one soluction is to filter the input and replace '.' with ','. Can you help me?

If you want validate in en locale e.g. 24.50 set locale option to your validator.

$this->addElement('text', 'prezzo', array(
    'label' => 'Prezzo (*)',
    'filter' => '',
    'description' => 'Il prezzo non è comprensivo di sconto, ma se previsto verrà calcolato',
    'required' => true,
    'validators' => array(array('Float', true, array('locale' => 'en'))),
    'placeholder' => 'Prezzo Pneumatico',
    'class' => 'form-control'
));