private function add($data, $language) {
        $parts = explode('-', $language); // To manage language with region (fr-CI, en-US, etc.)
        foreach($data as $key => $translation) {
            if (count($parts) == 1) {
                $this->translations[$language][$key] = $translation;
            } elseif (count($parts) == 2) {
                $this->translations[$parts[0]][$parts[1]][$key] = $translation;
            } else {
                throw new TranslationException('Invalid language');
            }
        }
    }