WordPress plug-in/PHP script - something like extranet

Hi there,

I want to create multi-language website for my new software. I want to include also login area for customers - customer will write down hi serial number or login/password and get some easy web page - just download zone, tickets review/submit, maybe some forum? Generally I’m looking for script (PHP or WordPress plug-in) which allow me to do it. WordPress plug-in will be best, because I can mix website layout with my extranet.

Any ideas?