/** The key of the configuration. e.g. ar=ar<br>
     * bg=bg<br>
     * bn=bn<br>
     * ca=ca<br>
     * ckb-iq=ckb-iq<br>
     * ckb_IQ=ckb-iq<br>
     * cs=cs<br>
     * da=da<br>
     * de=de<br>
     * el=el<br>
     * en=en<br>
     * en-ie=en-ie<br>
     * en_IE=en-ie<br>
     * es=es<br>
     * et=et<br>
     * eu=eu<br>
     * fa=fa<br>
     * fi=fi<br>
     * fr=fr<br>