Have to admit I always use sheeps! :o)

The English language sometimes seems to have been devised for the discomfiture of foreigners.

So will i -just need it in a poem now.

The "s" pluralization rule comes in from a later addition to English; nouns which come down from Old English AND are words which would be in daily use by an average speaker tend to hold on to older forms longer.

An average English speaker would use "sheep", "deer" (which meant "wild mammal-type-animal of any sort", not just the kind we now call "deer"), and "fish" frequently, and would generally think of them in terms of schools, herds, and flocks, rather than as individuals, so they were treated as conglomerate nouns.

Other common animals also were familiar enough to hold onto their older pluralization forms: cow/kine, ox/oxen, mouse/mice, goose/geese. There's no real hard-and-fast rule to figure out why some did shift to newer pluralization forms and others didn't, though -- why did "scip/scipu" change to "ship/ships", but "fisc/fisc" stayed as "fish/fish"? No idea.

Still, the general rule of thumb is that words which are in constant daily use are more likely to retain archaic grammatical forms, while words which are more rarely used are more likely to regularize. This helps explain why words like "is" tend to be irregular in languages which have them.

Re fish/fish, just to add to the confusion, there is also the word "fishes". It was always the miracle of the "five loaves and the two fishes" when I was in Sunday school.

Most of the time, "fishes" is used to mean "different kinds of fish."

But not always. There isn't an implication that the fishes in the miracle were, like, a sturgeon and a tuna.

Although, if they WERE a sturgeon and a tuna, it's pretty reasonable to feed a multitude.

Thanks. I've learned something.

If you think English plurals are irregular, you should see the variations in how Welsh forms plurals. :)

I think you're very brave. I'm useless at languages. I did a course in Urdu and have forgotten all of it.