Yeah,this whole issue is not a matter of Liberals vs. Consrvatives.Young woman is also accurate. The distinctive Hebrew word for ‘virgin’ is betûlâ, whereas ‘almâ means a ‘young woman’ who may be a virgin, but is not necessarily so. Cyrus H. Gordon, “Almah in Isaiah 7:14,” JBR 21, no. 2 (April, 1953): 106
What usually carries the weight for alma being understood as virgin is the Septuigent translation which collectively chose the Greek word parthenos which means virgin. It was in effect an interpretive choice based on their vast experience as scholars. Matthew followed this line of usage as would have been expected but he also wanted to highlight the uniqueness of the birth of Jesus.
It seems to me to be a prophetic word for the time and also for the time of Jesus. Both translations are reasonable and both require further explanation. Of course in my opinion.
I'll give a snip from the NET notes regarding almah:
"The word seems to pertain to age,not sexual experience,and would normally be translated 'young woman.' The LXX translator(s) who later translated the Book of Isaiah into Greek...rendered the Hebrew term by the more specific Greek word (parquenos), which does mean 'virgin' in a technical sense. This is the Greek term that also appears in the citation of Isa 7:14 in Matt 1:23."
In the Net text for Is. 7:14 it renders it "young woman."
In the NASBU,the footnote says:"Or young woman."
In the NIV foonote it says :"Or young woman."
In the NLTse the same kind of footnote :"Or young woman."