sinsir, как вариант...
<script language ="JavaScript">
function selChange(seln) {
selNum = seln.city.selectedIndex;
Isel = seln.city.options[selNum].text;
alert("Выбрано: "+Isel);
if (Isel == 1)
{var as = "de";}
else
{var as = "ru";}
document.getElementById('test').innerHTML=as;
}
</script>
<form>
<label>Выберите город: </label>
<select name="city" onchange="selChange(this.form)">
<option>1
<option>2
<option>3
<option>4
</select>
</form>
<div id='test'></test>