var txt1 = new Array();
var txt2 = new Array();

txt1[0] = "ようこそ！";
txt1[1] = "Welcome to";
txt2[0] = "へ";
txt2[1] = "!";

count = 0;

function changeTxt(){
  count = count % 2;
  document.getElementById("welcome").childNodes[0].nodeValue = txt1[count];
  document.getElementById("to").childNodes[0].nodeValue = txt2[count];
  count = count + 1;

  setTimeout("changeTxt()",2000);
}