"She is buying nineteen blue plates."
Translation:Ona kupuje dziewiętnaście niebieskich talerzy.
Could someone please tell me why it's 'niebieskich' rather than 'niebieskie'? Is it in the genitive case?
Yes indeed. Most numerals actually take Genitive..
The ones that take simple Nominative are: 1, 2, 3, 4 and those ending with -2, -3, -4... apart from those ending with -12, -13, -14. And that's just the beginning of Polish numerals, because then of course the function they serve in the sentence changes the case of the whole 'numeral+noun' phrase...
I realize the number words are here so we can learn them but in real life situations would a Pole write out the numbers or use just numbers: Ona kupuje 19 niebieskich talerzy
You might need to say this sentence aloud, instead of writing it (although that is pretty unlikely I admit).
In the French course you can put the numerals instead of spelling out the words and it is accepted. I always do this for numbers and times when I am writing the English translation of the French text since I don't need the practice at learning "a quarter to five" is the same as "4:45". You could check and see if this works for the Polish course too.
As far as whether a Pole would bother to spell out the number we'll have to wait for a native to say. It's probably the same as in English though, sometimes you would and sometimes you wouldn't. It depends on the writing style and personality of the writer. I spell out numbers as often as I use the numerals when writing something that is primarily word based with a number here and there.
that depends, I prefer to write the whole number/amount in more formal things. I think it looks better. Also you have to write "Słownie" on any money related documents.
And you know only situation where I can imagine anybody writing down "Ona kupuje dziewiętnaście niebieskich talerzy." are : texting, and some kind of story/novel. SMS 100% use digits, books 99% use words
IMO, having to pronounce number names is rather crucial language skill.
But in writing it generally depends on how big the number is.
Probably a stupid question, but why is it not 'talerzów'? It's genitive plural right? Is 'talerz' an exception?
It might be because the words ending with -rz get the -y ending in plural genitive. I'm not sure if that's the actual rule, but it seems to check up for the few examples I can think of off the top of my head.