"He is my neighbor."
Translation:C'est mon voisin.
it is not a matter of sense but of language:
I think that "Il est" or "c'est" could both be used, depending on the context. "C'est" is certainly more informal and more common especially in present tense, but "il est" is also correct and certainly not unheard of. My impression is that "C'est" conveys its English equivalent of "That's" or "It's" or "Voila" or answering "Qui est-ce?" but "Il est" is more formal and respectful, or if you are answering the question "Qui est-il?" For example, I would never introduce my boss as, "Je vous presente M. Leclerc. C'est mon patron." I would not give a presentation and say, "Ghandi est une figure historique. C'est une source d'inspiration." I mean, if I had a friend over and they said, "C'est quoi, ce bruit?" or "C'est qui, ce mec?" I would say, "C'est mon voisin." If I were testifying at a trial, and a lawyer asked me, "Comment connaissez-vous M. Lafleur?" I would say, "Il est mon voisin."
But I'm not a native speaker. Nothing I can find online seems to give a definitive answer either. Any tips on this?
Modern French has definitely adopted that formula, though.
Maybe take a look at this page: http://www.frenchtoday.com/blog/cest-versus-il-elle-est
If you don't want to say: "Je vous presente M. Leclerc. C'est mon patron.", which I can understand, you have other options, like: Je vous présente mon patron, M. Leclerc".
If you don't want to say: *"Ghandi est une figure historique. C'est une source d'inspiration.", you can say: "Il représente (reste, est devenu, constitue...) une grande source d'inspiration."
To answer the lawyer: "Comment connaissez-vous M. Lafleur ?", you could say "Monsieur Lafleur est mon voisin".
So, a rule is a rule, but you can move around it if you don't feel comfortable with its application.