class Test {

    constructor() {
    }

    /**
     * Loads translations
     */
    async _loadTranslations() {
        console.log("Loading tanslations");
        let response = await fetch('data.json');
        let json =  await response.json();
        return json;
    }

    async translate(key, language) {
      if(!this.translation){
        this.translation = await this._loadTranslations();
       }
       return this.translations[language][key];
    }

}

(async() => {
    console.log("translation", await (new Test()).translate("MEGA_MENU_CMD","de-DE"));
})();