The Vatican enters the social networking platform Twitter this weekend by launching a feed in six languages http://twitter.com/news_va_en.   Twitter is a free service that allows users to send or receive brief messages — or “tweets” — through a computer or smartphone. The Vatican also launched a new Web page (www.resources.va) on which it will offer multimedia information on current topics. The Vatican also has its own Youtube channel (www.youtube.com/vatican) in 4 languages. Zenit