KohanaPHP » Kohana v3.x

When $translate === FALSE, __() function doesn't call, its OK. We doesn't need translating, but placeholders like :field and :param{X} should be replaced with current fieldname and rule params.
I think, errors() method use something be like this:

...
    if ($translate == TRUE)
{
        if (is_string($translate))
    {
            // Translate the message using specified language
            $message = __($message, $values, $translate);
        }
        else
    {
            // Translate the message using the default language
            $message = __($message, $values);
        }
    }
    else
{
        // Replace message keys with fieldname and rule params
        $message = strtr($message, $values);
    }
    ...