"Good evening, it is me."
Translation:Buonasera, sono io.
I am a little confused by "sono io". It seems to me to be a bit of a tautology "I am I". In English the "it" in "it is me" could be something other than a person, such as the disturbance caused by an approaching person, and by declaring "it is me" you state that you are the disturbance rather than some marauding squirrel. This typical English usage (squirrels can be molto aggressivo) doesn't seem to me to fit with "sono io", but better "è il io" or "it is I". Imagine the conversation ...
Me: "Good evening, I am I." My Friend: "Hello my friend with a strong sense of self identity, and good evening to you, but what was that noise just now? You better come inside before you're attacked by squirrels."
Me: "Good evening, it is I!" My Friend: "Good evening and welcome my overly grandiose friend. Thank God it is only you, as for a moment I thought we were to be overrun by squirrels."
In summary, please explain the choice of "sono io" over "è il io".
Some things just don't translate to English perfectly. Literally it does translate to "I am I". But it's /meaning/ is "it is me". Just like you don't say "il mio nombre e' Abby", even though that is the literal translation of "my name is abby". Instead you use "mi chiamo Abby" (I call myself Abby).
Io sono = I am. Io sono io = I am I/me. Sono io = it's me. In Italian, sometimes the subject is dropped in spoken language for the very reason you have all asked this question. To say "I am I" would be redundant, whereas to drop the initial "io" indeed changes the literal translation to simply "it is I/me". "È il io" would not serve the same function. A translation of your suggested "è il io" would give a meaningless statement. In any sense, è = is, il = the, io = I. Thus, your suggestion would literally translate to something like "it is the I." In Italian one would never use "il" when they themselves are the subject it modifies. Recap: Io sono una mela = I am an apple. Sono io, Marcello = it's me, Marcello.
The thing is it just doesn't make grammatical sense in Italian to pair a subject with a verb that isn't conjugated for that subject, so "è io" - (it) is I, just doesn't make sense to an Italian speaker, so instead the first-person singular (io/I) form of essere is used - sono. But this doesn't really mean what you suggested - "I am I".
Think of it more as "it am I", the it being implied because romance languages like Italian tend to not have direct equivalents of the "it" that we would use in this context in English. "It am I" may not sound correct to you as an English speaker, but as you find out with language learning, direct translation does not always work. And I assure you that the usage by DL is correct. It's the same as in Spanish if you know any. To say "It's me", you would say "Soy yo", not "Es yo". Sometimes there are just weird language things that you have to accept.
So remember, think of it as "It am I". It may not sound right to you, but it's the best way to think of it. I hope this helps!