What difference in pronunciation is there between "macię klucz" and "macie klucz"?
I find a big difference between the "-a" and the "-ą" sounds at an end of a word--there's a clear n intonation when "-ą" is used to denote third person plural. I can also detect a clear "n" when the "-ę" comes in the middle of the word (e.g., in "mężczyzna," the "-ę" sounds like "ahn" in the French word "manger." But when "-ę" is used to denote first person singular, I'm having a hard time picking that up.
There is no such word like "macię". It is "mam" for first person singular. Final "ę" is often denasalised so often there can be only a little difference between final "ę" and "e".
Word final „ę” is pronounced pretty much like a normal „e”. You need to learn where it comes grammatically if you want to reliable transcribe it from speech.
I understand your question, completely. I find that when Polish is spoken, often, first-person vs third person of the word sound exactly the same. For example, a word like "get" in Polish (dostac and the "c" should have the dot above it) will "sound" the same in first person (dostaje - and the "e" has a tail on it) vs third person (dostaje - the "e" has no tail". However, when I annunciate the first person version of the word, I do include the "e with a tail" sound. I do not understand why it gets lost when most people are speaking the language.
As a learner you are more careful with your speech than most of the natives. I approve of that ;)
The recording doesn't sound like Macie, but like Marcie. Duolingo team, please correct the sound.
Sounds fine to me, apart from the overall intonation.
We would love to correct the sound, but that's nothing we can really do. The TTS technology is clearly not that advanced yet, at least the technology available for Duolingo to purchase.