get language redirect url in language switch button.js

/************************************************************
<div id="myDropdown" class="dropdown-content">
  <a href="/ja/index.html" id="JapaneseLanguage">JAPANESE</a>
  <a href="/en/index.html" id="EnglishLanguage">ENGLISH</a>
</div>
*************************************************************/

$( document ).ready(function() {
  var ja = document.getElementById("JapaneseLanguage");
  var en = document.getElementById("EnglishLanguage");
  var currentPath;
  var currentUrlPath = window.location.pathname;
  if ( (window.location.pathname.lastIndexOf('/en/')) == 0 ) {
    currentPath = currentUrlPath.split("/en/")[1];
  } else if ( (window.location.pathname.lastIndexOf('/ja/')) == 0 ) {
    currentPath = currentUrlPath.split("/ja/")[1];
  } else {
    currentPath = "index.html";
  }
  ja.href = '/ja/' + currentPath;
  en.href = '/en/' + currentPath;
});