How to do logic in struts tags?

[[EMAIL PROTECTED]]

I need to pass a request parameter value to a form action. If using a hidden
fild, I can do it like <s:hidden name="lang" value="${lang}"/> as the tag
doesn't allow an experssion as its value. How can I get around it?

Another question is how to use <s:if ...> or other struts tag to do this
logic:

<%

   if ("en".equals(request.getParameter("lang")) {

     ...

   } else {

      ...

   }

%>

Thanks a lot.