"Isaiah 7:14: ‘Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.’ Christians say that this verse is a prophecy of Jesus' birth to a virgin. Virgin in this verse is a mistranslation of the Hebrew word almah, which actually means ‘young woman.’"
You say that miraculous sign was that "a young woman" would give birth. How could that be a "sign" from God? Billions of young women have given birth. The sign was that a virgin would conceive. That’s a sign.