function getBrowserLang() {
  if (document.all) {
    return navigator.browserLanguage;
  } else if (document.layers) {
    return navigator.language;
  } else if (document.getElementById) {
    return navigator.language.substr(0,2);
  }
}
function switchLang() {
  var lng = getBrowserLang();
  if (lng != 'ja') {
    location.href = './english/index.html'; 
  }
}