validation › Validator.php

<?php
require_once dirname(__FILE__) . '/../i18n/I18n.php';

class Validator
{
    // ...

    private function getErrorText($field, $rule, $arg)
    {
        $key = I18n::hasKey("error_{$rule}_{$field}") ?
            "error_{$rule}_{$field}" : // error_required_first_name
            "error_{$rule}";           // error_required

        $translatedField = ucwords(I18n::__($field));

        return I18n::__($key, ['field' => $translatedField, 'arg' => $arg]);
    }

    // ...
}