$xp = XML::XPath->new(filename => 'config.xml');
$xp->setNodeText(qq~/conf/section[\@name="$name"]/description[\@lang="$lang"]~, $val);

##</code><code>##

$xp->find(qq~/conf/section[\@name="$name"]/description[\@lang="$lang"]~)->get_node(1)->string_value();

##</code><code>##

open(XML, ">config.xml");
print XML $xp->find('/conf')->get_node(1)->toString;
close XML;