"The dog does not write."
Translation:Pies nie pisze.
Pies is a subject here(since it is the dog and not someone else who is not writing) and subject of the sentence should be in nominative normally.
That said, "Ten pies nie pisze", should probably be accepted(usually it is an overkill to translate the as "ten/ta/to", but there are some rare contexts where it is OK), so if it isn't, please report it.
Everything, people will probably understand it, but i orde to say it properly you have to decline world 'pies'. This is part of polish grammar and it is utterly difficult. Ten pies. (this dog), Tego psa (this dog), Temu psu, (this dog), and for the plural is also more. As you see in English this is all this same, it is not in Polish and I think it can take more than 10 years to learn it perfectly (assuming that you live in Poland and talk with people everyday.). You have to 'feel' it how you say it. I myself if I wouldn't be Polish I will never be able to learn this language, it is just too difficult. Even now I have University degree and I make many, many mistakes in polish.
What a stupid sentence, try to make some sentence people can really use like (Ten długopis nie pisze, potrzebuję nowy.) or (Mój długopis się wypisał, pożyczysz mi swój?) This make sense.
Please don't confuse people trying to learn Polish here, „potrzebować” always without a fail connects with genitive case – „Ten długopis nie pisze, potrzebuję nowego” is the only correct way to say it in Polish.