German definitely did not cause those curious plurals. We know for sure Old English had them itself from Proto-Germanic, and it makes a lot more sense for a language to retain irregular forms for words that are used very often, than to loan grammar, which is a relatively rare occurrence.
EDIT: How do you type asterisks here? Escaping with a backslash doesn't work, nor does using three in a row
for reference
cold https://en.wiktionary.org/wiki/Reconstruction:Proto-Indo-Eur...
call, cry, (yell?) https://en.wiktionary.org/wiki/Reconstruction:Proto-Indo-Eur...
https://en.wiktionary.org/wiki/child from PIE g(')elt- (“womb”)
from Proto-Indo-European gel- (“to ball up, amass”). according to the PGmc page https://en.wiktionary.org/wiki/Reconstruction:Proto-Germanic...
but
https://en.wiktionary.org/wiki/dolphin
says from δελφύς (delphús, “womb”), which says from
From Proto-Indo-European gʷelbʰ- (“womb”)
I'd offer German "Quälgeister" as modified reflex of the latter. Also "Quell" is synonym for off-spring. Well, spring is a direct translation of "Quelle", i.e. source. Coincidence? Cry fits in, too.
I do not believe the dolphin theory, though. I guess tail-fish is more likely. they have a penis after all, which is way funnier in general, perhaps to funny for low brow scribe type doctors. Ancient Greek δελφίς (delphís) lends itself for φίς (phís) > fish. cf. https://en.wiktionary.org/wiki/fin IMHO
any questions?
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It's not like German were "at fault". English grew out of a common ancestor with nowadays German.
So, Ochsen -> Oxen, Maenner -> Men
(Slightly unrelated) So if you look at Scotland and Ireland, they've get some really interesting things in their dialects. die "Kirche" in German is a "church", in some dialects in scotland, it's a "kirker". Or in old dialects in Ireland, "children" is sometimes spoken as "childer".
EDIT: I retract my theory on the relationship between children and kindern :)