So, your point of view is that everyone who is important will know English enough to participate in an English-only site, and people who are not able to do so, must be excluded, just so the English-speaking ones have an easier life.
The motto of Stack Exchange is Make the world a better place, not Make the world a better place for English speakers.
As I understood the current concept of Stack Exchange, every topic which finds a community will have a chance in the Area51 process. And "Italian-language questions about Programming" are certainly now off-topic (or otherwise not allowed) in Stack Overflow (and every other SE site), so it is not a duplicate.
If there are enough people who want to ask/answer in Italian about programming problems, they should have their own site.
Yes, this will draw some people away who otherwise would have posted on other sites, but this also happens if you open more sites on other topics in English (for example, I'm quite less active on SO now after crypto.SE opened - my total SE time is limited). On the other hand, more new people will participate.
Your example with Adam is a straw man: Nobody is forced to translate his own questions/answers (though if one posts in two languages, one should be polite enough to put links). If someone wants to get reputation by translating an answer, let him do so.