Isaiah 7:14, why did LXX translate H5959-young-woman as G3933-virgin?

[TonyChanYT]

JPS Tanakh 1917, Isaiah 7:

14 Therefore the Lord Himself shall give you a sign: behold, the young woman [H5959] shall conceive, and bear a son, and shall call his name Immanuel.

There are 3 Hebrew words with similar meanings:

1, H5959, almah, 7 occurrences. A young woman or a virgin. H5959 is ambiguous.

2. H1330, betulah, 50 occurrences. Virgin.

3. H5291, 63 occurrences. Damsel, a young unmarried woman, may or may not be a virgin. Ruth was one.

Brenton Septuagint Translation:

Therefore the Lord himself shall give you a sign; behold, a virgin [G3939] shall conceive in the womb, and shall bring forth a son, and thou shalt call his name Emmanuel.

G3933 παρθένος appears 15 times in the NT.

Cambridge Bible for Schools and Colleges:

The Christian Fathers … resolutely upheld the correctness of the LXX., although the post-Christian Greek versions of Aquila, Theodotion and Symmachus agree in rendering the word by νεᾶνις.

Why did LXX translate H5959 as παρθένος (G3933)?

Cambridge explained this way:

It is almost incredible that the use of the word παρθένος for ‘almâh in so important a connexion should be due to mere laxity on the part of the translator.

The LXX translators did it deliberately. Why?

More probably it expresses a belief current in Jewish circles that the Messiah was to be born of a virgin. A good deal of evidence has been adduced to shew that such an expectation actually prevailed amongst both Alexandrian and Palestinian Jews [35], and if it existed it could hardly fail to influence the exegesis of this prophecy.

Two centuries before Christ, the LXX translators believed that Isaiah 7:14 prophesied the virgin birth of the coming Messiah.

 

[Prycejosh1987]

I believe that Mary was a virgin in the sense that she never had sex. I assume she was a teenager and Joseph was an older cousin in His late 20s. He cannot be been younger he cannot have been older.

 

[Ronald Nolette]

JPS Tanakh 1917, Isaiah 7:


There are 3 Hebrew words with similar meanings:

1, H5959, almah, 7 occurrences. A young woman or a virgin. H5959 is ambiguous.

2. H1330, betulah, 50 occurrences. Virgin.

3. H5291, 63 occurrences. Damsel, a young unmarried woman, may or may not be a virgin. Ruth was one.

Brenton Septuagint Translation:


G3933 παρθένος appears 15 times in the NT.

Cambridge Bible for Schools and Colleges:


Why did LXX translate H5959 as παρθένος (G3933)?

Cambridge explained this way:


The LXX translators did it deliberately. Why?


Two centuries before Christ, the LXX translators believed that Isaiah 7:14 prophesied the virgin birth of the coming Messiah.

Also an almah (young girl) was assumed to be virgin in Jewish culture so it is a correct interchange.

 

[The Learner]

hebrew young woman
In Matthew virgin