.en, .nl { display:none; } /* hide all elements with a language class */
.en:lang(en), .nl:lang(nl) { display: initial; } /* show those elements that match their language class */

/* colorize the selected language */
li.language.english:lang(en), li.language.dutch:lang(nl) {
    background-color: blue !important;
}
li.language.english:lang(en) a, li.language.dutch:lang(nl) a {
    color: white !important;
}