I’m often asked this question, so it was nice to come across this paper by Jan Joosten online.
Joosten is an excellent scholar in Aramaic, Syriac, Greek, and Hebrew. This is a worthwhile (and sane) introduction to the issue.
Readers will note that eventually Joosten gets to Matthew 1:23, where Matthew quotes Isaiah 7:14. He makes the point that to Hebrew or Aramaic readers, the term almah would have been ambiguous (i.e., they wouldn’t have thought of virgin). That’s overstated. On lexical grounds, it has merit, but it’s a fact of the OT that almah — due to its interchange with betulah, the more precise word for virgin, and the culture, an almah could be conceived of as a virgin. Here’s a short popular essay I wrote on the subject, posted here some time ago.
At any rate, Joosten doesn’t bring up Matt. 1:25. Two verses after his quotation of Isa 7:14, Matthew makes the comment that Joseph didn’t “know” Mary until after Jesus was born. If the gospels had been written in Hebrew or Aramaic, that’s an idiom that would have been completely understood by an audience speaking either language as a denial of sexual intercourse between Joseph and Mary, far more readily than Greek speakers.