Who said "Man's greatest wish is to have never been born"?  This may be a
paraphrase but the meaning is the same.  I always assumed it was one
of the French existentialists, and a friend thinks it was Sophocles,
but I haven't been able to find information indicating it was either.

Please reply with the name of the speaker and proof in the form of the original
source and its context.  If it's not originally in English, a few competing
translations would be appreciated.

A similar quote to what you posted is:
"It is man's greatest crime to have been born"...
--by Pedro Calderon de la Barca

http://www.anvari.org/fortune/Quotations_Alphabetic/339.html

I found that.  It's not it, but thanks.

Perhaps your friend who is attributing this to Sophocles is thinking
of the teachings of Silenus, as mentioned in "Oedipus at Colonus":

"Silenus was described as the oldest, wisest and most drunken of the
followers of Dionysus, and was said to be the young god's tutor.

When intoxicated, Silenus was said to possess special knowledge and
the power of prophecy. The Phrygian King Midas was eager to learn from
Silenus and caught the old man by lacing a fountain from which Silenus
often drank. As Silenus fell asleep, the king's servants seized and
took him to their master.

Silenus shared with the king a pessimistic philosophy: that the best
thing for a man is not to be born, and if born, should die as soon as
possible."

http://en.wikipedia.org/wiki/Silenus

"Dionysus, at whose festival tragedy was performed, is a newer god,
introduced from the East, who, it is believed, demanded orgiastic
worship and confrontation with reality, not the illusion that masks
the truth of existence. With Silenus as teacher and then companion, he
would have learned that the best of all things for a man 'was not to
be born, not to be, to be nothing' and the second-best was 'to die
soon'. This is echoed in Sophocles by the chorus of elders at Colonus:

Say what you will, the greatest boon is not to be;
But, life begun, soonest to end is best,
And to that bourne from which our way began
Swiftly return."

http://pages.britishlibrary.net/simon.mahony/sa.html