The present consensus on the origin of the so-called “Russian” recension of the Book of Esther (in Slavonic) goes back to the works of Moshe Altbauer, Moshe Taube, and Horace Lunt (Altbauer, Taube 1984; Taube 1994; Taube, Lunt 1998) and is enforced by Alexander Kulik (2005, 2008). According to this view, the work is translated from a Jewish recension in Greek somewhere in the Middle Ages. The terminus post quem for the Greek original is provided by Kulik: 8th cent., the date of establishment of the fast of Esther on 13 Adar, which is mentioned in 9:17 of this recension only. Kulik mistakenly refers to a much later witness but his dating is basically correct but limited to the Rabbinic tradition (cf. First 2010); the proto-Rabbinic tradition represented in the 1st-st century Megillah Ta‘anit forbade fasting on the “Nicanor Day” 13 Adar (cf. 1 Mac 7:47-49; 2 Mac 15:35-36). According Altbauer, Taube, and Lunt, the Slavonic version was created by South Slavs between the 10th and 13th cent.
This consensus is challenged by Irene Lycén (2001), who put forward completely new (in comparison with earlier studies by Meshchersky and Alekseev) argumentation for an original in Hebrew. The weakest point of the hypothesis on the Greek original is linguistic features of the Slavonic version: sporadic appearance of /s/ as a rendering of /t/ in transliterations. For Lycén, this is a feature of Ashkenazim orthoepy, thus allowing placing the Sitz im Leben of the translation in the 13th-century Ruthenia. The adherents of the “Greek” hypothesis need to put forward a conjunction of two suppositions (each of them rather feeble; thus, the likelihood of the conjunction is vanishing): the Greek translator was trying to preserve the Ashkenazim orthoepy, whereas this orthoepy has been widespread among the Byzantine Jews long before the 13th cent. (instead of the Western European Jews since the 13th cent.).
My solution of the problem is following:
1. The Greek text is a Second Temple Jewish recension (probably, Alexandrinian). The earliest mention of the “Fast of Esther” is that among the so-called “Jewish festivals” within the Ethiopic Easter computus, where the encapsulated Jewish calendar goes back to the Hellenistic Judaism of Alexandria (and does not contain Maccabean commemorations).
2. The linguistic peculiarities of the Slavonic translation are explainable with supposition that the original was a Syriac translation from Greek.
Cf. Veder 2010 on the Glagolitic protograph.