The LXX dates back to before the time of Jesus. It’s a Greek translation, but the pronouns of whom is striking at who shows masculine.
eg:
αυτος σου τηρη-σ-ει κεφαλ-ην και συ τηρη-σ-εις αυτ-ου πτερ(ν)-αν
he of-you(M) will-strike head(F) and you will-strike of-him heel (F)
So, by the pronouns – it is his heel which is being struck.
Therefore, I really don’t imagine that Luther changed it.
A couple of small points:
The head of the serpent is female – though the YOU of the serpent is male.
The heel of the man is feminine also – though it belongs to him.
Those just happen to be the genders of those words and the same genders show up on men’s heels all over the OT. etc.
It is possible that a female is meant, because mankind includes women – but when describing a single woman, this is the exception and rare.
Biologically Women do not have seed (of their own) for it is referring to that which comes from a man. The seed is analogous to the clay (slip) which Adam (earth/earthy) was formed out of. But, scripture seems to imply that when the two become one flesh, in marriage, the seed becomes the woman’s.
This can be seen in Genes 16:10 where Hagar is told a similar thing to Eve –
eg: that her seed (children) would be greatly multiplied.
Genes 16:10 και ειπεν αυτη ο αγγελος κυριου πληθυνων πληθυνω το σπερμα σου και ουκ αριθμηθησεται απο του πληθους
The Catholic church has the right to interpret the final meaning of scripture – but as an apologetic, I wouldn’t go charging out with accusations on Genesis 3:15 to protestants, nor to Jews with respect to Gender.
I don’t know Hebrew, but comparing Genesis 3:15 and 16:10 using a lexicon:
The Hebrew root word for seed is.
This word is generically singular – I suppose. Because It is used where Eve speaks of Seth.
In Genesis 3:15 the word is third person (her) feminine, eg: her seed.
http://www.messiahtruth.com/gen315_files/image018.jpg,
zar’ah***
***and in Genesis 16:10 the word is second person (you) feminine. eg: her seed.
http://www.messiahtruth.com/gen315_files/image016.jpg,
zar’ech
The only thing the Greek gives an advantage on, is that it refers to the seed as a male (singular). So, it does support the idea of a messiah being in the Jewish mindset in the years before Jesus came; at least Greek speaking Jews.
(Although I am unsure of how much weight it would carry in an argument.)
A similar problem shows up in Galatians 3:16 which refers to the use of the singular by Abraham in Genesis 22:18 – in Greek it
is singular, but it can also be collective – eg: it might refer to all his children as “seed” , and it might also refer to his one son, Isaac, who is multiplied…
Note, that doesn’t make Paul “Wrong” or the church “Wrong” on Genesis 3:16 – it is just that a more immediate explanation also exists.
Pax Christi,
–Andrew.
P.S.
The Hebrew of Gen 22:18 has:
וְהִתְבָּרְכוּ בְזַרְעֲךָ, כֹּל גּוֹיֵי הָאָרֶץ, עֵקֶב, אֲשֶׁר שָׁמַעְתָּ בְּקֹלִי.
Which looks like “ben-zar” son of seed? perhaps?

I don’t know, but that might be more explicit than the Greek if it is.