Therefore, “almah” could mean either “young woman” or “virgin”. However, given the context of the verse, a young woman giving birth to a child would not be a sign at all especially when this child will be called “God with us” and two chapters later in Isaiah 9:16 “Mighty God”. That is why given the context, even the scribes when translating “almah” to Greek in the Septuagint, chose to translate the word as “virgin”.
What Judaism teaches
Isaiah 7:14 Therefore, the Lord, of His own, shall give you a sign; behold, the young woman is with child, and she shall bear a son, and she shall call his name Immanuel.
Almah has been mistranslated in the Christian bible as “virgin” when it actually means “young woman”.
“Judaism says that the Messiah will be born of human parents, and possess normal physical attributes like other people. He will not be a demi-god, and will not possess supernatural qualities. In fact, an individual is alive in every generation with the capacity to step into the role of the Messiah.” Maimonides – Laws of Kings 11.3