I always wanted to tried this, finally I got a client who was willing to do this for his site.
So I added 3 domains to drupal site. Then i selected "Domain name only" as the Language negotiation options and then inputed domains for each language in language configuration, pretty easy. Then comes the server part, with VPS this is not a problem, I edited my site file (virtual host file) which is in etc/apache2/sites-avaialble
and added
ServerName www.yourdomain.com
ServerAlias www.yourdomain.com
ServerAlias www.french-yourdomain.fr
ServerAlias www.german-yourdomain.de
In addition to this, you'll also need to point the domain name server (DNS) to your server for all the domain names in different languages before this so you dont get apache error. Rememebr to reload/restart apache for this to go into effect.