prova cosi':

codice:
<form name="modifica" method="post" action="scrivimodifica.asp">

<select size="1" cols="4" name="linguaccia" onchange="this.form.langue.value=this.form.linguaccia.options[this.form.linguaccia.selectedIndex].value">
<option value="i" selected >Italiano</option>
<option value="p">Portoghese</option>
<option value="e">English</option>
</select>

<input name="langue" size="1" type="text" />
</form>
ciao