I see 2 problems with your adapted version of my example:

1. You shoul use query_form to encode the request as I did in my example. If you do not, you will have to worry about handling special characters (like spaces) in the request yourself.

my $site=new URI::URL 'http://translate/lhsl.com/greenacres.dll';
$site->query_form(text=>$text, pair =>$pair, domain=>$domain, interface=>$interface);

2. $WWWresult is not the text returned by LWP; it is an HTTP::Response object. The object contains the page conent (in $WWWresponse->content) in addition to any LWP errors, etc...