Cyrus H. Gordon notes that an Ugaritic tablet from 1400 BC where a lunar goddess is called the Ugaritic counterparts of 'almah (young woman) and bethulah (virgin).
Cyrus H. Gordon, "'Almah in Isaiah 7:14," Journal of the American Academy of Religion, 21, no. 2 (April 1953): 106
Ever since the publication of the Revised Standard Version there has been a storm of debate over the translation of 'almah in Isaiah 7:14 as "young woman" instead of the King James "virgin." 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.
Little purpose would be served in repeating the learned expositions that Hebraists have already contributed in their attempt to clarify the point at issue. It all boils down to this: the distinctive Hebrew word for "virgin" is bethulah, whereas 'almah means a "young woman" who may be a virgin, but is not necessarily so.
The aim of this note is rather to call attention to a source that has not yet been brought into discussion. From Ugarit at 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. (For the translation, see my Ugaritic Literature, Rome, 1949, pp. 63-64.) 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 bethulah "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.