Translation:There are French athletes in this group.
As a native English speaker, I find Duo's insistence on including "there" in this answer is too strict. Likewise, "In this room there are five tables," which I would more naturally say as "In this room are five tables." Leaving out "there" doesn't make it incorrect English usage or change the meaning.
This sentence may be strange without ‘there’, but in a great many cases, it not strange at all to leave out ‘there’, and it is never grammatically wrong to do so. It seems contrary to duolingo's style to turn down swathes of valid translations for purely didactic reasons. At any rate, I think it is wrong to suppose that English speakers don’t understand ‘in x is y’ very well. After all, it appears in any children’s story e.g. “Deep in the forest is a witch’s house“ and everyday language “In this box is a key which you can use…”
According to (the ever-helpful) Kundoo here: https://forum.duolingo.com/comment/27753949
В этой группе есть французские спортсмены. - There are French athletes in this group (among other people).
"В этой группе французские спортсмены" - This group consists of French athletes (all of them are).