<html>
<head>
<script type="text/javascript">
window.onload = function() {
document.getElementById('select').onchange = function() {
document.getElementById('text').value = this.getElementsByTagName('option')[this.selectedIndex].innerHTML;
};
};
</script>
</head>
<body>
<select id="select">
<option>RU</option>
<option>EN</option>
</select>
<input id="text" type="text" />
</body>
</html>