Validate polish postcode

functions.php

<?php 

/**
 * Validate polish postcode. "-" is required.
 *
 * @param bool   $valid .
 * @param string $postcode .
 * @param string $country .
 *
 * @return bool
 */
function wpdesk_validate_polish_postcode( $valid, $postcode, $country ) {
	if ( 'PL' === $country ) {
		$valid = (bool) preg_match( '/^([0-9]{2})-([0-9]{3})$/', $postcode );
	}

	return $valid;
}

add_filter( 'woocommerce_validate_postcode', 'wpdesk_validate_polish_postcode', 10, 3 );