Weird sentence. "All birds lay an egg"? Maybe "All birds lay eggs in May"? (Although I can't say anything about factual accuracy of course... haha...

I can say something about factual accuracy. It's completely untrue, since none of the male birds lay eggs. :)

I agree that it's a bit weird sentence. If it's really too weird I can change it to "eggs", but it won't be a translation of the Dutch sentence anymore (which it was translated from, and which I don't want to change, because it's a saying). Funnily, all languages that I can understand enough of to tell, use "eggs"...

FWIW, usage of the plural varies between languages; for example, "Open your books, children!" (plural) could be "Öffnet das Buch, Kinder!" (singular) in German because each child only has one book.

So a translation of "eggs" in English could still be a faithful translation of a Dutch "ei" if Dutch works similarly.

Hmm, okay. Then maybe "lay eggs" is better. I can't say, cause I don't know how weird exactly the current sentence sounds. Whoever feels called to change it, can do so. :)

(This does make me wonder how you'd best express in English the difference between all birds laying an undefined number of eggs and each bird laying just one.)

>(This does make me wonder how you'd best express in English the difference between all birds laying an undefined number of eggs and each bird laying just one.)

In English you could say:
"All birds lay eggs" (could be one egg or undefined number)
"Every bird lays an egg" (one egg)
"Every bird lays eggs" (undefined number)
And, of course, it's not "all / every" bird as only females lay eggs.