Shadal writes that his first printed book, Kinnor Naim, was printed by the Vienna press of Anton von Schmid, and that he ought to explain how he came to print books. So he backtracks and writes that on March 5, 1821 the Austrian emperor Franz I commanded his Jewish subjects of Trieste to produce a siddur with an Italian translation facing the Hebrew. Initially a prominent member of the community, Joseph Eliezer Morpurgo, said that he would translate it and print it, but after beginning it he discovered that because of his work he didn't have the time. He asked other people, including a local teacher named Joseph Tivoli, none of whom were willing to undertake it without significant monetary renumeration, and they specifically objected to the fact that he intended to have it printed with his name. Then he asked Shadal, who agreed (without asking what he would be paid, or if his name would appear on it).
To make the job easier for him, Morpurgo gave him the Italian translation of the Sephardic version of the prayers by the famed poet Salomone Fiorentino, and told Shadal that all he needed to do was to follow it, and just make the necessary changes according to the Ashkenaz version. Thus he immediately began to work on it and he quickly realized that he could not use Fiorentino's version since he disagreed with it so frequently, so he made the translation entirely fresh.
From time to time Morpurgo would bring the already-translated sheets to Rabbi Avraham Eliezer ha-Levi's home (he was the Chief Rabbi of Trieste, and also had been Shadal's rebbe), so that he could review them since his approval was needed before sending them to the printer. One time Yoseph Tivoli came to the rabbi's house (to tutor his grandson) and he saw those sheets and recognized Shadal's handwriting. He immediately told the rabbi that Morpurgo was lying to claim that he was the translator, because really it is being translated by Shadal. Furthermore, Shadal is a total epikoros, because he wrote a commentary on Kohelet, which denies that King Solomon was the sole author. That night Morpurgo came to read new sheets to the rabbi, but the rabbi didn't want to listen since it was made known to him that they were written by an epikoros, and he didn't want to give his haskama to it. The rabbi confronted Morpurgo about his deception, and the latter tried to calm him by pointing out that what was written was written, and didn't the rabbi examine and approve of every section so far? If he found no defect, then why couldn't it be printed with his haskama? Morpurgo was very important, and the rabbi had no reply to the point.
Although Shadal's own name was besmirched, something good came of it, because thoughr it it became known that he was the translator (which he had not told a soul). It had become became impossible for Morpurgo to hide it. So Morpurgo told him that he'll write "Translated by Shadal" on the title page, and Shadal was gratified by it. He then told him what had happened, and because he was so important he could override the rabbi's anger. (I guess this was Morpurgo's consolation prize.) In that same year the first part was printed in Vienna, and with his name on it, his name became known throughout Italy - but this wasn't because of self-promotion, but because of the efforts of one who spoke lashon hara about him through jealousy, because he did not get the chance to do the translation for money.
In any case, what about Salomone Fiorention's translation? As it happens, the siddur of Salomone Fiorentino (1742-1815), who was a famous poet in Italy, was printed in 1825 and is online. Here is a picture of Fiorentino, followed by the title page of his siddur:
How did he translate mei raglayim? Not suprisingly, at this point, the answer is according to the tradition, which will not countenance the literal meaning:
His translation is "eppure l'acqua di Raglaim avrian prodotto l'istesso effetto?" while Shadal's is "eppure le acque del fonte Raglaim sarebbero state piu efficaci?" Same idea, different words.
You can see that Fiorentino included a footnote marked (d) - this is one of exactly nine footnotes in the siddur!
The gist of what he writes here is that Raglaim are potent, acidic waters. If I understand him correctly he is saying that although this isn't the plain sense of the term, many writers insist that these foul waters were produced by a fountain called Raglaim, which had the potency of the hard root of the Ziporen. Although, as we have seen, the most famous source for this explanation is in the Kol Bo, he does not cite it. Yet in the prior footnote he cites Col Bo in explaining יין קפריסין.