Since I learned the Polish word, I always say and write złotych (or złoty etc. obviously where appropriate), even when the rest of the sentence is in English. It's the Polish name for a Polish thing that we don't have in amy English-speaking area, so why should we anglicise the name for it or have our own name for it? I mean, yeah ok, maybe accept it without the stroke through the l and undeclined in an English sentence if some people don't have the diacritics on their keyboard or feel weird declining nouns when writing in English, but if I write złotych there's no way that's wrong, is it?
That's a good question. As 'ł' in the default English sentence is concerned, I guess maybe there's no need to wait for the new course to change it - I changed it at least in those three sentences in this section.
As for "złotych" in the English version... on one hand, Wikipedia states that "The recognized English form of the word is zloty, plural zloty or zlotys." On the other, it uses the "złotych" form 48 times anyway. So... I guess it should be accepted. Added now.