function gwdev_checkout_fields_error($field, $key, $args, $value)
{
    if (strpos($field, "</span>") !== false && $args["required"]) {
        $error = '<span class="error" style="display:none">';
        $error .= sprintf(
            __("%s is a required field.", "woocommerce"),
            $args["label"]
        );
        $error .= "</span>";
        $field = substr_replace($field, $error, strpos($field, "</span>"), 0);
    }
    return $field;
}

add_filter("woocommerce_form_field", "gwdev_checkout_fields_error", 10, 4);