This post has been updated with an important new source.
The Tur (או"ח תק"פ), as part of his extensive list of days on which some people fast, writes: "On the 8th of (the month of) Teves the event with King Ptolemy (occurred)." Although the Tur doesn't elaborate, it's widely assumed that he's referring to Ptolemy II Philadelphus' commissioning 70 (or 72) Jewish scholars to translate the Torah into Greek. What's not clear is why that event should be the source of a fast day.
In fact, the story behind the translation - including the many miracles that accompanied it - is described in the Gemara (Megila 9a-9b) and, in greater detail, in Sefer Hakabala L'Ha'Raavad. But neither of those two sources suggests that the translation was a negative development. That has been attributed to a passage in the early work, Seder Olum:
"On the eighth of Teves the Torah was written in Greek in the days of King Ptolemy, and darkness came to the world for three days."
The problem is that, as far as I can tell, there is no such passage in Seder Olum. In fact, the versions we have of the book trace Jewish history from creation only until the invasion of Alexander the Great. Events involving Ptolemy Philadelphus, who was the son and successor of one of Alexander's generals, would presumably not have been included.
That passage does, however, appear in a different work that's often printed together with Seder Olum: Megilas Taanis. Megilas Taanis - which, like Seder Olum, dates back to the time of the Tanaim - is primarily a catalog of days on which one should either fast (because of corresponding historical tragic events) or avoid fasting (because of historical happy events).
So there is an authoritative source explicitly characterizing the Ptolemaic translation (known today as the Septuagint or תרגום שבעים) as, from a religious perspective, a disaster. Although, to be sure, there's no indication exactly what it was that concerned the rabbis.
But here's where things get weird. No, I'm not referring to the fact that many widely used Torah translations have appeared over the past century or so. To justify those, you could always argue that, disaster or not, excluding the millions of Jews who weren't fluent enough in Hebrew to read the Torah in its original language would have been a mistake. Instead, I'm talking about something that happened earlier. Much earlier.
Here's what it says in the Torah (Deut. 27:2-8)
"And it will be on the day you cross the Jordan to the land that God is giving you that you will erect for yourself great stones and cover them with plaster. And you will write on them all the words of this Torah...And you will write on the stones all the words of this Torah explained well."
And here's the Gemara in Sotah 32a (and 36a):
"...They brought the stones and built the altar and covered it with plaster and wrote on it all the words of the Torah in 70 languages"
Now I'll acknowledge that some (like ibn Ezra quoting "the Gaon") believed that only the number of mitzvos (מנין המצות) was written, rather than the entire Torah. But, as Ramban points out, various sources in Chazal clearly understood the stones to have contained multiple translations of the entire Torah text!
The Gemara in Sotah (35b) adds significant background to the narrative. For instance, it asks how non-Jews could be expected to read and learn from the translations if they were covered in plaster (the translations, that is, not the non-Jews). From this context, it’s clear that Chazal understood that the goal of the translations was to provide non-Jews with access to Torah teachings. And not just Greek-speaking non-Jews, either.
In that context, what was so awful about Ptolemy’s translation? Especially considering how the translation was undertaken by great Torah scholars with the support of miraculous intervention.
The following section has been updated from the original content based on important input from readers:
I could suggest the possibility that the Tur, when he wrote “the event with King Ptolemy”, wasn’t referring to that passage in Megilas Taanis. Perhaps he was instead thinking about one or more of the many acts of cruelty we know that Ptolemy unleashed against our people during his violent reign.
That wouldn’t explain the logic behind the Megilas Taanis itself, but at least it would help us with the more halachically-oriented sources. However, there’s a far more likely solution that’s based on 1:7-8 in Mesechte Sofrim:
מעשה בה׳ זקנים שכתבו לתלמי המלך את התורה יונית והיה היום קשה לישראל כיום שנעשה העגל שלא היתה התורה יכולה להתרגם כל צרכה: חשוב מעשה בתלמי המלך שכנס ע"ב זקנים והושיבם בשבעים ושנים בתים ולא גלה להם על מה כנסם נכנס לכל אחד ואחד מהם אמר להם כתבו לי תורת משה רבכם. נתן המקום עצה בלב כל אחד ואחד והסכימה דעתן לדעת אחת וכתבו לו תורה בפני עצמה וי"ג דבר שינו בה
It happened that five elders wrote the Torah in Greek for King Ptolemy and that day was as difficult for the Jewish people as the day the golden calf was made, for the Torah was unable to be fully translated. A later event saw King Ptolemy gather 72 elders and place them in 72 houses without revealing the purpose for their being gathered. He said to them: “Write for me the Torah of Moshe your teacher.” God placed the idea in the hearts of each (of the elders) and they agreed to a uniform plan. And they each wrote the Torah with (identical) 13 changes…
So it seems that there were two attempts to translate the Torah to Greek, and only the first ill-fated attempt lead to tragedy. It’s pretty certain that the passage in Megilas Taanis we quoted above is, in fact, referring to this earlier translation.
Concerning the second attempt - clearly what we know as the Septuagint - there doesn’t seem to have been any problem at all.
The only point left to explore is what, exactly, Mesechte Sofrim meant by the words: “for the Torah was unable to be fully translated”. Here are some obvious possibilities:
That a literal translation was dangerous (something avoided through the miraculous changes in the Septuagint).
That these particular elders weren’t capable of doing a good job.
That they never even completed the task (something bound to anger their royal patron).
But in any case, it seems that there’s nothing intrinsically wrong with translating the Torah and, therefore, there’s no conflict with the story of the translations created under the authority of Joshua.
Perhaps at a later date, we might also consider whether the fact that the first five elders seemed to volunteer their translation services - rather than waiting for a royal commission - could also have played a role.