Q:

Translation to Greek

I just read in parashat ki tavo that the torah was translated into 70 languages and written on giant stones, yet the talmud says the translation of the torah to Greek many years later was considered a tragedy.
Why was it considered a tragedy if it was already translated into 70 languages?

A:

Actually, the earliest rabbinic sources present the Greek translation (the Septuagint) in glowing terms. In the Mishna, Megillah 1:8, Rabban Shimon ben Gamliel is quoted as having said that Greek is the only language, other than Hebrew, in which it is permissible to write sifrei Torah. Commenting on this, the Jerusalem Talmud (Megillah 71c) says that the sages checked and discovered that Greek is the only language into which it is possible to translate the Torah with its exact meaning.
Likewise, in the Babylonian Talmud (Megillah 9a), the origin story of the Septuagint is presented, and one which testifies to the miraculous nature of its composition. This origin story is very similar to the earliest extant text that testifies to the Septuagint's composition: a pseudepigraphic Jewish letter that purports to be written by Aristeas, King Ptolemy's bodyguard.
The reality is that, by the time we come to the composition of the extracanonical tractate, Sofrim, the attitude had changed rather dramatically. There, in Sofrim 1:6-7, it is explicitly said that sifrei Torah cannot be written in Greek, that it is impossible to translate the Torah into any other language without changing its meaning, and that the day on which the Septuagint was written (by no more than five elders!) was as hard for the Jewish people as the day on which the golden calf had been constructed.
The reason for this change of attitude lies in the fact that the Septuagint (which, in time, came to denote the translation into Greek of the entire Tanakh) was embraced by the nascent Church and used in anti-Jewish Christian polemic. A favourite in that regard was the translation of Isaiah 7:14, in which עלמה ('almah, "young lady") was rendered παρθενος (parthenos, "virgin").
By the time of the composition of minor tractate Sofrim, Christians had composed a number of anti-Jewish tracts, which utilised the Septuagint for the purposes of demonstrating Jewish stubborness in their rejecting Jesus. Perhaps the most graphic of these texts was a 6th century text (the same century in which Sofrim was composed), titled Disputatio cum Herbane Judaeo: "Disputation with the Jew, Hurban [from the Hebrew word, Destruction]". The author identifies himself as Bishop Gregentius of Tafra, in Yemen, but is only adopting that persona for the purposes of the text.
In it, he attributes the following sentiment to his invented Jew, Hurban:

Our fathers wrongly and capriciously translated the books of Israel
  into Greek so that you could take possession of the same and silence
  us.

Martin Hengel, The Septuagint as Christian Scripture: its Prehistory and the Problem of its Canon (ed. David J. Reimer; Edinburgh & New York: T&T Clark, 2002), 35.

With such attitudes as these, it was no wonder that the Jews came to view their Greek translation as a tragedy, to rule it out altogether as a liturgical text, and to undermine the earlier texts that spoke of the miraculous nature of its composition.

Emanuel Tov, "The Septuagint". Pages 161-188 of Mikra (ed. M.J. Mulder; Philadelphia: Fortress Press, 1988) - p163 in particular;
Norman Gottwald, The Hebrew Bible: A Socio-Literary Introduction (Philadelphia: Fortress Press, 1987), 121-122.

See also: Oded Irshai, "Confronting a Christian Empire". Pages 181-221 of Cultures of the Jews: A New History (ed. D. Biale; New York: Schocken Books, 2002). On p.203-204, he describes an attempt by Justinian in the 6th century, to ban study of the Mishna and to enforce that all Jews under his sphere of influence utilise the Septuagint if reading the Bible in Greek.

A:

From here (an essay based on the Likutei Sichot volume 24, pg 1-11).
The Talmud (tractate Sefer Torah, 1:8) says:

Seventy sages translated the Torah into Greek for King Ptolemy. That day was as difficult for the people of Israel as the day on which the [Golden] Calf was made; for the Torah could not be fully translated.

Read that essay for all the details, but in short:

The Lubavitcher Rebbe points out that it doesn't say the day the Golden Calf was worshiped, it says the day on which the [Golden] Calf was made.
The Golden Calf was made the day before it was worshiped, as Aharon told the Jews (Shemot 32:5) after he made the Golden Calf, "Tomorrow is a festival unto G-d!"
Aharon did not intend to use the Golden Calf as an idol, the people woke up early the next morning and worshiped it (Exodus 32:6).
So the day the Calf was made was a day of potential, it could have been good, it could have been bad (the next day it turned out to be bad)
So too, the day the Torah was translated into Greek by Ptolemy's decree had the potential to be good or bad, and in the end, the negative possibilities of the endeavor were averted, or at least greatly minimized.
the deeper meaning of the Talmud's words that the "difficulty" lay in that "the Torah could not be fully translated." Had the seventy sages fully -- that is, precisely and exactly translated the Torah into Greek, it would have been exposed to misinterpretation and distortion. It was only because they succeeded in presenting Ptolemy with a less than literal translation that this tragedy was averted. Indeed, their translation yielded the positive result of bringing G-d's word to the Greek world, and showing the way for the subsequent translators of Torah who would spread the light of Torah to all peoples and cultures of the earth.

The essay also analyzes another statement in the Talmud, (tractate Shabbat Shabbat 13b and 17a):

A count was conducted, and it was found that the sages of Shammai were more numerous than the sages of Hillel. Eighteen ordinances were enacted on that day... and that day was as difficult for the people of Israel as the day on which the [Golden] Calf was made.

