Translation:The country is rich in copper, iron, gold, and silver.
Well, I'm only fluent in English, not native, but usually when we use lists of things, we don't repeat the preposition for the other nouns. I don't think it would be incorrect English strictly speaking, but it sure feels odd.
Except maybe when you want to make an emphasis on one or some of the objects. A native will probably clear this out for us.
I said "The country is rich in copper, in iron, in gold, and in silver" and got it right. I was being overly cautious because the french sentence has "en" in front of all of them, but normally you would omit the "in" in english purely out of convenicence, but it's not wrong if you have it. It's just a wee bit clumsy.
I am a native English speaker, and ". . . in silver" seems fine to me. In writing, you would probably use parallel construction, that is, you'd use "in" before the first item on the list, and then either skip it for all the others, or use it for all the others. But "The country is rich in copper, iron, gold and in silver" doesn't sound wrong to me, just somewhat unusual.
I tend to agree that in listing a number of items separation by comma is sufficient . However I, and I am sure many others, have fallen foul of DL's pedantry (for example requiring a definite article to be translated even though normal English would not) so in this case I translated every "en". It all speaks of the irritating inconsistency sometimes manifested.