Would it be an idea to add to the hover notes that this is (and some other words are) informal?
"Dzięki" is less formal, I would use it talking with a friend, but not for example in a shop.
according to sjp.pwn.pl Dziękować is loan word from "staro-wysoko-niemieckiego"(literally old-high-german) danken, denke (now Dank)
It was religious (Deo gratias facere), and came to Poland form Czech with Christianity, They still exist in Czech and Slovakian and though Polish went to Ukrainian and Russian.
Belarusian, yes--дзякуй (dzjakuj), but not Russian--спасибо (spasibo). "Spasi" means "save," also a Christian concept.
Is спасибо then an abbreviated form of "God save [you]!" - you thank people by blessing them?
I think you meant "danke". "denke" means think. denken - to think (ich) denke - (I) think
It almost sounds like there is an N sound between e and k. Could someone write its pronounciation in Cyrillic letters? Thanks.
I don't think one can write it in Cyryllic, there is no corresponding sound. ę is palatalized e, and I guess it sounds a bit like an additional N - which makes some less educated natives sometimes write it 'dzienki', which is clearly an orthographic mistake. It is closest in pronunciation to 'eu', for example in Spanish pronunciation of "Europa".
If it's at the end of the word, it usually is less clear and a bit more like simple e, for some people even totally like simple e.
The letter 'ę' is a nasalized version of 'e'. Tip to pronounce the letter is to pronounce the syllable 'en' in the word 'sense', but don't let your tongue touch the roof of your mouth. Modern Slavic languages that use the Cyrillic alphabet do not have that sound, although that letter existed in Old Church Slavonic as the letter 'ѧ'.
Isn't 'dz' an alveolar affricate (d͡z)? The audio sounds more like a palatoalveolar affricate (d͡ʒ).
It's followed by i, so in fact the whole thing is not a digraph but a trigraph: "dzi". Therefore yeah, it's palatalized.
Sanskrit is indeed older than old high German, but most of the languages of the world did NOT originate from sanskrit (the hindi languages do, but no European language does). Sanskrit and other Indo-European languages share the ancestor though, proto-Indo-European, so the 'dan' in 'danke' and 'dhaan' in 'dhaanyavaad' could be cognates if they both originally meant 'to give'. It would find it hard to believe that polish would have borrowed a sanskrit word though.
When spoken dzięki mają thanks, it should not be headed an error if the exclamation mark is left off
Duolingo doesn't assess interpunction, so that seems like a bug. Can you provide a screenshot?