htaccess rewrite based on hostname or domain name

Question

I have two different domains (let\'s say www.site1.com and www.site2.com) that point to the same hosting server.

I need the two different domain names because I want

Answer 1

Lawrence Cherone - Thank you, that one works like a charm! Now it works:

RewriteCond %{HTTP_HOST} ^www\.site1\.com [NC] 
RewriteRule ^(.*)$ index.php?lang=it [NC,QSA] 
RewriteCond %{HTTP_HOST} ^www\.site2\.com [NC] 
RewriteRule ^(.*)$ index.php?lang=en [NC,QSA] 

Of course I check the www redirect before this rule.

Thank you!!