adding Zend\Translator resources via zf2 global config, also see http://framework.zend.com/manual/2.3/en/modules/zend.validator.messages.html#using-pre-translated-validation-messages

global.php

<?php

return [

    // the following assumes that you are using composer
    // and that your main application entrance point (i.e. public/index.php) changes the working directory 
    // to the one containing the 'vendor' dir, like in ZendSkeletonApplication.

    'translator' => [
        'locale' => 'it',
        'translation_file_patterns' => [
            [
                'type'          => 'phpArray',
                'base_dir'      => 'vendor/zendframework/zendframework/resources/languages',
                'pattern'       => '%s/Zend_Captcha.php',
                'text_domain'   => 'zend_validate',
            ],
            [
                'type'          => 'phpArray',
                'base_dir'      => 'vendor/zendframework/zendframework/resources/languages',
                'pattern'       => '%s/Zend_Validate.php',
                'text_domain'   => 'zend_validate',
            ]
        ],
    ],

];

Module.php

<?php

namespace Application;

use Zend\Mvc\MvcEvent;
use Zend\Validator\AbstractValidator;

class Module
{
    public function onBootstrap(MvcEvent $event)
    {
        $application    = $event->getApplication();
        $serviceManager = $application->getServiceManager();
        $translator     = $serviceManager->get('translator');
        
        AbstractValidator::setDefaultTranslator($translator, 'zend_validate');
    }
}