private function diffMissing(array $toTranslations, array $fromTranslations, $locale)
    {
        $diff = array_diff_key($toTranslations, $fromTranslations);

        if (count($diff) === 0)
            return;

        foreach ($diff as $transKey => $transValue) {
            $this->addMissing($locale, $transKey);
        }
    }