The word "virgin" doesn't even exist in Hebrew, how can Isaiah say virgin birth?

Isaiah 7:14 - "...Behold, a virgin shall conceive, and bear a son..."

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.

15 Butter and honey shall he eat, that he may know to refuse the evil, and choose the good.

Isaiah 7:14-15

Hebrew word for virgin here is "Almah"
Another Hebrew word that is similar is "Bitulah"
Some argue that Almah means "maiden" and that Bitulah would be a better work. However both can be translated either way.

Example of use of "Almah":

43 Behold, I stand by the well of water; and it shall come to pass, that when the virgin(maiden) cometh forth to draw water, and I say to her, Give me, I pray thee, a little water of thy pitcher to drink;

44 And she say to me, Both drink thou, and I will also draw for thy camels: let the same be the woman whom the Lord hath appointed out for my master's son.

Genesis 24:43-44 (KJV)

Example of use of "Bitulah":

6 And the damsel was very fair to look upon, a virgin, neither had any man known her: and she went down to the well, and filled her pitcher, and came up.

Gen 24:16 (KJV)

Both of the above verses refer to the same person, Rebekah"
In the line "...neither had any man known her", Bitulah as "virgin" is redundant. This would seem to indicate that Almah would be a better example of "virgin" and Bitulah better as "maiden".
In fact in the NJPSV (New Jewish Publication Society Version) out of the 50 times "Bitulah" is used 31 times it is "maiden"
The Septuagint (LXX) translated "Almah" as Parthenos - which does mean Virgin in Greek, and indicates those Jewish translators took the meaning as virgin.
In reality there is no clear word in Hebrew that definitively is translated one way or the other all the time. Both Almah and Bitulah have been translated as Virgin and Maiden.
However in both cases the expectation is an unmarried women, implied to be chaste.