private function getArticleContentMap(string $sourceLanguage, string $targetLanguage): ArticleContentMap
    {
        if (!array_key_exists($key = $sourceLanguage . '->' . $targetLanguage, $this->articleContentMaps)) {
            return $this->articleContentMaps[$key] = new ArticleContentMap(
                $this->getArticleMap($sourceLanguage, $targetLanguage),
                $this->logger
            );
        }

        return $this->articleContentMaps[$key];
    }