protected function getTranslation(array $translationData, $default = '')
    {
        // undefined locale
        if (empty($translationData)) {
            return $default;
        }

        // current locale matched
        if ($this->locale && isset($translationData[$this->locale])) {
            return $translationData[$this->locale];
        }

        // default locale matched
        return $this->defaultLocale && isset($translationData[$this->defaultLocale]) ?
            $translationData[$this->defaultLocale] :
            $default
        ;
    }