http://home.earthlink.net/~markdlew/comm/turandot.htm
(the words and meaning of Nessum Dorma) call for a bit of discussion, I think.
The libretto of Turandot doesn't translate easily because it's so heavily poetic. Not just the lyrics, but the entire plot, which (as many befuddled listeners have complained) doesn't make much sense if taken too literally. Forgive me if I recap most of the plot, but the poetry of the aria is too tied up in the story not to discuss it....
As you probably know, Turandot is the beautiful cold-hearted femme fatale princess who lures love-struck princes to their death. Anyone who wants to marry her is asked three riddles: If he answers them right he gets to marry her, but if he doesn't he is beheaded. This is stated at the very beginning of the opera as "the law" ("La legge è questa:"). It is not so much a government decree as a mythopoetic law, almost like a magic spell, which no one in the kingdom -- not the emperor, not Turandot, not the ministers -- can go against.
In the first act Calaf, the "Unknown Prince", rings the gong, signifying his declaration as a suitor to Turandot. In the second act he correctly answers the three riddles. According to the law, Turandot now has to marry him, even though she doesn't want to. But instead of claiming his prize, Calaf now poses a riddle of his own, saying to her: Tell me my name before morning, and at dawn I shall die. ("Dimmi il mio nome, prima dell'alba! E all'alba morirò!")
Take this literally and it's a dumb move on his part -- he's already won, why should he give her another chance to get away? -- but of course nothing in this opera makes sense if taken literally. Naturally, the Prince's statement is poetic. Furthermore he WANTS to "lose" the game; he wants her to tell him his name and he wants to "die." Besides being another instance of the Lohengrin/Rumpelstiltskin guess-my-name game (which can be traced to religious beliefs of pre-Christian Germany) the Prince is telling Turandot of his true goal. (Notice that he does not say "IF you guess my name....") He doesn't want her to marry him reluctantly; he wants to defeat her cold-hearted defensiveness and have her fall in love with him. This is, in fact, exactly what happens at the end of the opera, and the metaphors are quite explicit. The veil which Turandot wears (and which Calaf rips) is described as "cold" ("fredda"), for instance.
So when the Prince poses the riddle, the name he refers to is not "Calaf", but rather the name she will ultimately give him: "Amor" ("Love"). That is, he wants her to love him. This, incidentally, also makes sense out of the scene where Liù is killed. When Turandot orders Timur to reveal the name, Liù says, "The name that you seek I alone know." ("Il nome che cercate io sola so.") Huh? Timur doesn't know his own son's name?? Literally, of course he does know; but poetically, Liù's statement is correct, because she's the only one who is in love with the Prince.
Where the Prince says "then I shall die", he really means "die" in the sense of lose himself completely to true love. Yes, I know, death-equals-love sounds like a pretty perverse metaphor, but it's a persistent one (and more common in Romance languages than it is in English). For an example in English (albeit written by an Italian), when Laetitia in The Old Maid and the Thief sings, "O sweet thief, I pray, make me die," she isn't hoping that he'll murder her....
The aria "Nessun dorma" is near the beginning of Act 3. At the end of Act 2 Turandot hasn't yet figured out all this love poetry business, and still thinks that she just has to get someone to reveal the Prince's name and then she can chop off his head. So she puts out a decree that no one in Peking is allowed to sleep until the name is revealed.
Act 3 opens in gloomy night with lugubrious chords in the orchestra (technically, minor chords with augmented 7ths and 11ths). Some heralds are announcing Turandot's decree, "Tonight no one in Peking sleeps" ("Questa notte nessun dorma in Pekino"), and the chorus gloomily repeats the words "no one sleeps" ("nessun dorma"). In the first words of his aria, the Prince is repeating the words of the chorus. The G major chord that opens the aria is the first optimistic-sounding chord we've heard since intermission and it breaks through the gloom like the light of dawn.
The translation, finally:
The Prince:-
No one sleeps, no one sleeps...
Even you, o Princess,
In your cold room,
Watch the stars,
That tremble with love
And with hope.
But my secret is hidden within me;
My name no one shall know, no, no,
On your mouth I will speak it*
When the light shines,
And my kiss will dissolve the silence
That makes you mine.
Chorus :-
No one will know his name
And we must, alas, die.
The Prince:-
Vanish, o night!
Set**, stars!
At daybreak, I shall conquer!
* "Dire sulla bocca", literally "to say on the mouth", is a poetic Italian way of saying "to kiss." (Or so I've been told, but perhaps a native speaker can confirm or deny this.) I've also been told that a line from a Marx Brothers movie -- "I wasn't kissing her, I was whispering in her mouth" -- is a conscious imitation of the Italian phrase.
** "Tramontate" literally means "go behind the mountains", but it's the word Italians use for sunset and the like. It's also a word Turandot uses after Calaf kisses her: "E l'alba! Turandot tramonta!" ("It's dawn, Turandot descends!") This suggests yet another mythopoetic theme which pervades the Turandot libretto -- the sun god's defeat of the moon goddess -- but I won't get into that....