public function removeTranslationUnit(tao_helpers_translation_TranslationUnit $translationUnit)
    {
        $tus = $this->getTranslationUnits();
        for ($i = 0; $i < count($tus); $i ++) {
            if ($tus[$i] === $translationUnit) {
                unset($tus[$i]);
                break;
            }
        }
        
        throw new tao_helpers_translation_TranslationException('Cannot remove Translation Unit. Not Found.');
    }