"Behold, a young woman shall conceive, and bear a son"? Hold the front page. Young women have babies all the time.
But virgins do not. Now, that would be something worth prophesying.
Of course almah means "virgin". Why else did the Septuagint translators, who were Jews, render it as parthenos? So much for there having been no Jewish expectation that the Messiah's mother would be a virgin.
But in any case, if there had been no such expectation, then there would have been no reason for the Evangelists to make it up, so the doctrine works either way.
The only other notable occurrence of this unusual word in the Bible is in Proverbs 30:19, where it contrasts with the adulterous woman in the next verse. Anything other than "virgin" would be meaningless.
No, a similar masculine word is never translated as "male virgin", but that is because there is no such physical state as male virginity. There is arguably no such thing, and there was certainly no concept of it at the time.
Faced with a widely believed claim that the prophecy had been fulfilled, the rabbis had to fall back on sneering that, "It doesn't really mean that."
But of course it did.
And of course it does.