function change_lang (lang) {
    var oForm = document.getElementById('lang_form');
    appendHidden(oForm, 'language', lang);
    appendHidden(oForm, 'return_url', window.location);
    oForm.submit();
}
function appendHidden (form, name, value) {
    var newElem = document.createElement('INPUT');
    newElem.type = 'hidden';
    newElem.name = name;
    newElem.value = value;
    form.appendChild(newElem);
}