hola ya eh podido lograrlo,
Código PHP:
<select name="dm_idioma[]" multiple style="height: 200px;">
<option value="it" >Italian</option>
<option value="ko" >Korean</option>
<option value="zh-CN" >Chinese (Simplified)</option>
<option value="zh-TW" >Chinese (Traditional)</option>
<option value="pt" >Portuguese</option>
<option value="en" selected>English</option>
<option value="de" >German</option>
<option value="fr" >French</option>
<option value="es" >Spanish</option>
<option value="ja" >Japanese</option>
<option value="ar" >Arabic</option>
<option value="ru" >Russian</option>
<option value="el" >Greek</option>
<option value="nl" >Dutch</option>
<option value="bg" >Bulgarian</option>
<option value="cs" >Czech</option>
<option value="hr" >Croatian</option>
<option value="da" >Danish</option>
<option value="fi" >Finnish</option>
<option value="hi" >Hindi</option>
<option value="pl" >Polish</option>
<option value="ro" >Romanian</option>
<option value="sv" >Swedish</option>
<option value="no" >Norwegian</option>
<option value="ca" >Catalan</option>
<option value="tl" >Filipino</option>
<option value="iw" >Hebrew</option>
<option value="id" >Indonesian</option>
<option value="lv" >Latvian</option>
<option value="lt" >Lithuanian</option>
<option value="sr" >Serbian</option>
<option value="sk" >Slovak</option>
<option value="sl" >Slovenian</option>
<option value="uk" >Ukrainian</option>
<option value="vi" >Vietnamese</option>
</select>
Código PHP:
foreach ($_POST['dm_idioma'] as $idioma){$dm_idioma .= $idioma.',';}
gracias de todos modos