A common argument raised against the virgin birth" and against the New Testament's reference to Isaiah 7:14, is that the Hebrew word "almah" does not mean virgin, and Jews do not believe in such a thing as a virgin birth.
Archaeological findings show that the Hebrew word "almah" refers to a virgin. The possibility of a virgin birth is upheld by open-minded Jewish sages and scholars, even those who are not believers in Jesus.
Here is the verse in question in two different translations:
New International Version
Therefore the Lord himself will give you a sign: The virgin will be with child and will give birth to a son, and will call him Immanuel.
Jewish Publication Society Version
Therefore the Lord Himself shall give you a sign: behold, the young woman shall conceive, and bear a son, and shall call his name Immanuel.
Cyrus Gordon, a leading Jewish scholar who was formerly Professor of Assyriology and Egyptology, Dropsie College, wrote:
The commonly held view that "virgin" is Christian, whereas "young woman" is Jewish is not quite true. The fact is that the Septuagint, which is the Jewish translation made in pre-Christian Alexandria, takes 'almah to mean "virgin" here. Accordingly the New Testament follows Jewish interpretation in Isaiah 7:14.
...From Ugarit of around 1400 B.C. comes a text celebrating the marriage of the male and female lunar deities. It is there predicted that the goddess will bear a son....The terminology is remarkably close to that in Isaiah 7:14. However, the Ugaritic statement that the bride will bear a son is fortunately given in parallelistic form; in 77:7 she is called by the exact etymological counterpart of Hebrew 'almah "young woman"; in 77:5 she is called by the exact etymological counterpart of Hebrew betulah "virgin. Therefore, the New Testament rendering of 'almah as "virgin" for Isaiah 7:14 rests on the older Jewish interpretation, which in turn is now borne out for precisely this annunciation formula by a text that is not only pre-Isaianic but is pre-Mosaic in the form that we now have it on a clay tablet.
-- "'Almah in Isaiah 7:14," Journal of Bible and Religion 21 (1953), p. 106.
Jewish sages have sometimes had something to say about the possibility of a virgin birth:
Abraham Farissol, medieval Jewish sage:
We cannot deny the possibility that God, may He be blessed, could create in a virgin, even one whom no man has known, for He created everything out of nothing.
-- quoted by Daniel J. Lasker, Jewish Philosophical Polemics Against Christianity in the Middle Ages (New York: KTAV/ADL, 1977), p. 153.
The Nizzahon Vetus, medieval work of polemics:
Granted that the prophet said that a virgin would give birth to a son. So what? There is, after all, no doubt that the Lord's hand is not incapable of fulfilling his will and desire, and that he is a ruler who can do whatever he wishes...."
-- David Berger, The Jewish-Christian Debate in the High Middle Ages: A Critical Edition of the Nizzahon Vetus (Northvale, NJ: Jason Aronson, 1996, © 1979), p. 103.
Contemporary scholar Adam Kamesar:
The doctrine of the virgin conception was not attacked per se. The possibility that a woman might conceive with her virginity intact, though by means of normal fertilization, is an occurrence which is conceded in the Talmud.
-- Adam Kamesar, "The Virgin of Isaiah 7:14: The Philological Argument from the Second to the Fifth Century," Journal of Theological Studies, n.s., vol. 41 part 1 (April 1990), p. 51.
Note: Some say that the Septuagint mentioned by Cyrus Gordon and many others, is not a Jewish document. Is this true?
The Septuagint is the translation into Greek of the Hebrew Scriptures, made for the benefit of Greek-speaking Jews in Egypt. This is the version that translated "almah" as "parthenos," which nearly always means "virgin." Some have discounted its value, claiming that except for the Torah, the Septuagint is a Gentile Christian translation. However, that is not the view of most scholars.
Suzanne Daniel, Associate Professor of Judeo-Hellenistic Literature, Hebrew University, Jerusalem:
On the Torah portion of the Septuagint:
It is assumed that the project was initiated by the Greek-speaking Jewish community itself, which needed a version of the Pentateuch for worship and instruction.
On the Prophets and the Writings portions of the Seputuagint:
It is...generally held that the versions of the Former and Latter Prophets must be placed before the end of the third century B.C.E., and that at least some of the Hagiographa were already translated at the beginning of the second century B.C.E., since the prologue to the Greek Ben-Sira (132 B.C.E.) refers to an already existing version of "the Law, the Prophets, and the other writings." It is therefore accepted that a complete version of the Hebrew Bible existed at least at the beginning of the first century C.E.
-- "Bible," section "Greek: The Septuagint", Encyclopedia Judaica.