Elle attend ce moment depuis longtemps.
Duolingo translates this as "She waited for this moment for a long time." or "She has been waiting for this moment for a long time."
Why isn't it "Elle attendait..."?
It seems like a trick question, and this isn't the only example where present tenses are being used to describe past events.
"Elle attend ... " is perfectly (no pun) correct if that is what is meant. "Elle attendait ... " is the imperfect verb tense. You use this when the event you are speaking about occured in the past and also ended before the present. So, in English the difference between i) "attend" and ii) "attendait" is along the lines of:
i) "She has been waiting a long time for him to propose. He's going to ask her over dinner?"
ii) "She had been waiting a long time for him to propose. When is the date of the wedding?"
The French is quite clear that she is currently waiting for "this moment" to arrive (which could be imminent or still some time in the future), but that she started waiting a long time ago. That doesn't put it in the past tense.
"Elle attend ce moment depuis longtemps." = "She has been waiting for this moment for a long time." Correct, no question. Source: Collins Robert French Dictionary 4th Ed. - see usage of "depuis". I won't even try to defend the alternative translation offered by Duolingo, as I have no authoritative source and I wouldn't put it like that.
@Agreed. The "waited" sentence is definitely awkward, and needs to be "has waited_for/awaited" or "has been waiting".
The construction itself is not wrong e.g. "She waited for the taxi for a long time", but there's a fulfilment of a past desire or expectation here that breaks this example in the same way as "She waited for this man/baby/job for a long time" just doesn't work.
It's an interesting example!
@Gersois : the sentence "she waited this moment for a long time" does not "feel" right to me. I was taught English by teachers insisting on the fact that "for+duration" and "since+date" needed a present perfect in English matching a present in French (or a pluperfect matching a preterit if the action is entirely in the past). Summary: "elle attend ce moment depuis longtemps" => "she has awaited (or has been awaiting) this moment for a long time" - "elle attendait ce moment depuis longtemps" = "she had awaited (or had been awaiting) that moment for a long time". That's the way I learnt English. What to you think?