If you think re-translating the liturgy of the Mass is a problem, try re-translating the Bible.
Recently, the Confraternity of Christian Doctrine issued a revised edition of the New American Bible (NABRE). I haven't picked it up yet; I do have a couple of copies of the NAB, though for most of my work here I use the Catholic edition of the Revised Standard Version (RSV-CE, which I usually abbreviate RSV).
Although there are plenty of minor changes—especially the much chuckled-over switch to "treasure" from "booty"—the one change that causes the most concern is the retranslation of almah in Isaiah 7:14 from "virgin" to "young woman". In this chapter, God speaks through Isaiah to Ahaz, the king of Judah, and tells him to ask for a sign. Ahaz refuses: "I will not tempt the Lord!". Then he turns to the people and says:
Listen, O house of David! It is not enough for you to weary men, must you also weary my God? Therefore the Lord himself will give you this sign: the [almah] shall be with child, and bear a son, and shall name him Immanuel.
In the retelling of the prophecy in Matthew 1:23, the Hebrew almah is translated by the Greek parthénos, which was later translated in the Vulgate by the Latin virgō (from which we get "virgin"). Since NABRE only retranslates the Old Testament, it should still read: "Behold, the virgin shall be with child and bear a son, and they shall name him Emmanuel." Hence the problem: Is the woman of Isaiah 7:14 a virgin or not?
The problem of this translation goes back as far as the second century (see, for example, St. Justin Martyr [d. 165], Dialogue with Trypho 67). The argument goes something like this: almah doesn't strictly mean "virgin", for which Hebrew had the word bethulah. One non-Christian commentator even implies in a footnote that parthénos is a Christian interpolation and that other extant Septuagint texts of Isaiah use neanis (young woman). For my own part, I don't see why neanis couldn't have been a Jewish interpolation against Christians—but let's let that go.
There exists, of course, the question of whether parthénos was really specific to virgins; everyone I've read so far admits that there's not an exact one-to-one correspondence. Both parthénos and almah carried strong cultural presumptions of virginity, but have had uses where the girl in question had borne a child without the implication of a miracle.
Okay, we can agree on the basics: Both words essentially meant "maiden", an unmarried woman, of whom youth and hymeneal integrity could be reasonably inferred but not stated as a categorical fact. Yet if the almah of Isaiah 7:14 were sexually active, were there no Hebrew words to make that fact plain?
In fact, the Law of Moses declared that a man who took a maiden's virginity had to marry her, pay fifty shekels and could not divorce her (Dt 22:28-29). If she had somehow had sex before she were married and hadn't been caught, her husband on discovery could use that fact to not only divorce her but have her stoned to death (vv. 13-21). Not that such a reaction was unusual; a Roman paterfamilias could have his virgo killed for unchastity, and Vestal Virgins caught in flagrante delicto were buried alive.
So while almah did mean "young woman", we're justified on cultural grounds on presuming the almah's physical virginity to the extent that parthénos is a better translation than neanis. But it should also be kept in mind that, even granting that neither word automatically means "virgin", Mary's own virginity would still fulfill the prophecy, as she was of marriageable age and hadn't yet been officially taken into Joseph's house.
Furthermore, if Jean Carmignac (The Birth of the Synoptics) and Claude Tresmontant (The Hebrew Christ) were correct and Matthew was originally composed in Hebrew, then the use of parthénos to translate almah may not be due to possession of a Septuagint variant of Isaiah but rather to the translator's own choice when composing the Greek redaction of the gospel. (Possibly the first-ever example of "dynamic equivalence"?)
To a certain extent, the whole controversy puts the virginal cart before the prophetic horse. For to assert that almah didn't automatically mean "virgin" is not to prove that Jesus wasn't the meshiach or that he wasn't born of a virgin.
Both St. Justin's fictional Jewish challenger Trypho and our modern real non-Christian skeptic are engaging in a genetic fallacy, which tries to prove an assertion false by creating a counter-story of how the assertion began. Both Trypho and Richard Carrier presume that Matthew and Luke cribbed the Virgin Birth from pagan sources, then sought a passage in the Old Testament to make the Virgin Birth prophesied from centuries before. The argument sounds convincing … so long as you're not under any onus to prove that Matthew and Luke lied. But you can't justify presuming Matthew's or Luke's dishonesty without begging the question.
Stuart Chase's dictum (possibly taken from St. Ignatius Loyola) comes to mind here: "For those who believe, no proof is necessary. For those who don't believe, no proof is possible." If you're bound not to accept the Virgin Birth, then of course you're not going to accept that Isaiah prophesied it five hundred years before the fact; the presumption of virginity in the almah and the parthénos is an interesting cultural artifact, but no more than the presumption of virginity in "maiden" or das Mädchen.
The question of almah's presumption wouldn't even be an issue had not the Christians asserted from the beginning that Jesus was born of a virgin. But once Mary says that she has no relations with a man (Lk 1:34; lit. ou ginṓskō, "I do not know a man"), the event leaves the ordinary behind … and leaves the disbeliever grasping at any straw to deny it.
Otherwise, we'd presume the almah a virgin until she's proven guilty of fornication.