I voted yes - I see homeinmyshoe's point, but I also agree with Billi that those guys who would only post in the Italian forum would probably not post in the rest of the site anyway - while all those that already do will know that if they want to interact with the rest of the wonderful mobileread community will have to use English.
On the other hand, a dedicated Italian forum will allow everyone who feels that like it to discuss of e.g. Italian text in their original form - which might otherwise sound pretentious and pedantic in the general forum. Besides, having been living outside Italy for the past 18 years or so, I would relish the challenge of having to write in reasonable Italian instead of my lazy usual "Itanglish"