index.php shared from multiple languages is good or not?

on site:

www.tec.lisam.it/lang-en.html

if I click the homepage button (logo) it go always on

www.tec.lisam.it/index.php

but the same will happen also for all other languages, it is good or bad for google seo and how I could repair it? I'm using joomla 1.5.14 with joomfish and sef patch 1.5.14 , maybe I have to use some other sef extension?

I really do not think using the same homepage URL for all subdomains as well as different language versions would cause a problem.

It's like telling arriving on Google and then choosing from among tens of other country specific domains.