Translation:There are a few apples in the basket.
I just tried "is a pair of apples" and it was marked wrong. Perhaps "paar", although it resembles the English "pair", means something different.
This may have been rejected because you used the word "is".
In English, although the word "couple" literally means one pair, (or one partnership, if referring to people), the expression "a couple of...." is used as a loose term for a small number of items.
So it would be correct English to translate this as "There are a couple of apples in the basket"
Having said that, you might hear native speakers, at least in Britain, say "there's a couple of...." It's not good grammar, but probably a lot of us do it, informally, when in a hurry. :-)