Why is "Would you do me a favor?" not accepted here? Would the subjunctive be required?
(American English speaker) I think you're right about the reason. "Fai" is indicative. Another form would be required for "would."
Mi farebbe un favore? Is that used in Italian? "Will you do me a favor?" has an imperative twinge in American English. I wonder whether that's true in Italian as well for "Mi fai un favore?".
To be more gentle "Mi farebbe un favore/piacere?" or "Potrebbe farmi un favore/piacere?" sound better. That imperative twinge is present in italian as well
The most accurate one is the wordreference one, and for human voices the one on the example in forvo for "Piacere di incontrarti." by betpao. At least according to my dialect/accent, which keeps the first "e" closed. I'm not sure about linguistics, but if the "e" were to be open, the best examples would be for "piacere" by beahpb (which sounds actually a bit mixed) and for "Il piacere è tutto mio." by giorgiospizzi (completely open "e") on forvo.
In any case the duolingo one sounds a bit artificial and weird, you're right.
I've tried "you do me a favour?" and it was not accepted. Any explanations?
"You do me a favor"? is not correct in English. You need the
will you, would you, can you, could you, etc.
it seems like imperative should be used. in my language using indicative instead of imperative is rude.
In italian to ask for a favour one can say either "Mi faresti un piacere (+", cortesemente" to be even more polite)? or "Mi fai un piacere?" to be less polite but still correct. So either conditional, for optimal politeness, or indicative for neutral politeness. With the imperative "Fammi un piacere!" you can only order people to do stuff, so it's reasonable to say it's impolite.
Moreover, usage of imperative and a different intonation on this sentence results in "Ma fammi un/il piacere..!" (= "Ma per favore..!" = "Ma cosa vai dicendo?!") which implies the person you're talking with is talking bullsh*t, saying stuff that isn't true, etc and is often accompanied but that wonderful hand gesture some italians do with all the fingertips united and an up-and-down movement. In that sense, usage of imperative is highly discouraged if you're actually asking for a favour.
what about the imperative of Lei? Would «Mi faccia un piacere» make it more polite than «Fammi ...» ?
Ok, that makes sense: with the third person + imperative, there are some situational conditions in which it's accepted as neutral. First one that comes to mind is when an elderly person asks for something to younger people, officers of some sort, other...but I'm pretty sure anybody could use it.
Still, it already implies that the other person must accept, so you're not asking if he/she can, you're kind of forcing your hand on them.