What the texts say. The Masoretic Hebrew text reads ha-almah: “behold, the young woman shall conceive and bear a son.” The Septuagint reads hē parthenos, “the virgin.” St Matthew quotes the Greek almost word for word when he tells of Christ’s birth (Matthew 1:23). The Latin Vulgate follows with virgo. That the Septuagint reads parthenos, and that this reading is older than Christianity, is not in dispute (Very Strong).
What almah means. Almah is the feminine of a word for a young man. It describes a girl of marriageable age, not her sexual history. Hebrew has a word closer to “virgin,” betulah. So it is not accurate to say that almah by itself means “virgin” (Strong). But the line between the two words was not sharp. The same Greek translators rendered almah as parthenos in Genesis 24:43, speaking of Rebekah, whom Genesis 24:16 calls a betulah whom no man had known. And parthenos is not a strictly technical term either: the Greek of Genesis 34:3 calls Dinah a parthenos after Shechem had lain with her. Context, not dictionaries, decides.
An ancient argument. This is not a modern quarrel. Around AD 160 St Justin Martyr reports that his Jewish partner in dialogue, Trypho, read “the young woman” and applied the sign to King Hezekiah (Dialogue with Trypho 43, 67, 71). A generation later St Irenaeus objected to the newer Jewish Greek versions of Theodotion and Aquila, which rendered “young woman,” and appealed to the older Septuagint as made by Jews long before Christ came (Against Heresies 3.21.1).
What the Orthodox Church reads. The Orthodox Church reads the Septuagint as its Old Testament, so its Bible says “the Virgin.” It reads the prophecy as St Matthew did: the sign given to the house of David finds its full meaning in the birth of Emmanuel, God with us, from the Theotokos. Many scholars, including some Christians, also see a sign for Ahaz’s own day in the passage. That near meaning and Matthew’s fuller reading are not necessarily rivals.
How translations handle it. The KJV, NKJV and ESV read “virgin.” The NIV reads “virgin” with a footnote “young woman.” Several Catholic translations read “young woman”: the RSV Catholic Edition (with a footnote “virgin”) and the New American Bible Revised Edition. The NRSVUE reads “the young woman.” The Douay-Rheims, from the Vulgate, reads “a virgin.” The 1917 Jewish Publication Society version reads “the young woman.”
What it does and does not change. The Church’s confession that Christ was born of the Virgin Mary rests first on the Gospel accounts (Matthew 1:18–25; Luke 1:26–38, where Mary asks how this can be, since she knows no man). It does not depend on proving that almah means “virgin.” What is at stake is how Matthew reads Isaiah, and Matthew reads the Greek Scriptures the early Church received. Honest Christians do not need to overstate the Hebrew, and honest critics should not call the Septuagint a Christian invention.