I can see where Duolingo got "Novum Eboracum" = New York, even if it is only a linguistic joke
In fact, the Seal of NYC has 'Novi Eboraci' on it, and has done since the 17th century. DL didn't make this term up!
Here is the original seal of the Province of New York, created in 1669 (or 1664—I find conflicting references), with 'Sigill Provine Novi Eborac[i]':
'Eboracum' is the Latinised version of the original, Brittonic name of the settlement meaning 'of the yews'. This became 'Eoforwic' in Old English, which the Norse (who occupied York for a considerable period) turned into 'Jórvík', which Middle English subsequently turned into 'York'.
That will have very likely just been a phonological approximation leading to folk etymology, and started with Old English -wic ("Place") even before Old Norse -vic.
Eboracum was the Roman name for York in Latin, the titular seat of James II as Duke of York. York was founded by the Romans in 70 AD. https://en.wikipedia.org/wiki/Seal_of_New_York_City
California! I’m sorry, I just can’t do this anymore! I was so enjoying learning Latin (I’d moved off Spanish for a while in order to explore to what extent it was rooted in Latin.) That was until I got to this level; only to find it included Latin words for New York, Boston, and dare I say it, America! Can Duo not construct a sentence without American place names? Clearly not! With so many Italian place names to choose from, why on earth would one use place names from somewhere that was to lay undiscovered for another millennium. I’m off back to my Spanish, bye!
Perhaps the developers feel equally as sorry for recreating plausible Latin names and using one that is still featured on the New York state seal. Italian, however, should be equally as offensive since Dark Age Italian featured large amounts of Germanic imports by the Lombards on an already vulgar variant, save mentioning the natural variation that occurred well after the collapse of the polity.
If there were room to state that one 'can't do this anymore' that would be in the grammatical imprecision of the learning material. Exploration of the original intent in finding the correlation between modern Spanish and Latinate words is still possible.
You can always argue about the rightness or wrongness of translating proper names; I imagine that the Latin team probably took its position on this largely so as to avoid having to add numerous alternative translations on all sorts of cognate names people would inevitably submit (if you accept 'Steven', why not 'Steve'? Why not 'Stefan'? Why not Etienne? Etc.). This way they can concentrate on teaching Latin using Latin names.
The pronunciation is probably wrong considering even urban Romans made fun of the accents citizens gave from the provinces. The most famous case being Emperor Hadrian who was mocked while making a report to the senate. All efforts to reproduce authentic Italic are derivational and approximate, so the ecclesiastical account may take precedent.
after reading all positive and negative comments (surprised by the latter), I find there are 2 things worthy of mention (although obvious, they answer certain questions and objections):
this DuoLesson introduces adjectives and their gender, in this case neuter nominative Novum Eboracum; and
DuoLingo does this with an example that demonstrates the relevance of Latin, as in the historical account found in previous comments.
Non-Latin names do not take declension on Duolingo. York can be translated to Latin because York (Eboracum) was an important city in the Roman empire. (The emperor Constantine was proclaimed emperor there.) California is named after a fictional island which appeared in a novel by Garci Rodríguez de Montalvo.
Moreover, the locative was pretty much non-generative in Classical Latin (like the partitive in Russian, say, or irregular plurals in English). It is a holdover from a time where the language had a regular locative, prominent examples of which became fossilised in the standard form after it had fallen out of use generatively.
responding @Christyanbf's query: Why does New York have its locative noun version and California needs the preposition "in"?
As per rules explained previously in re "Romae" and "in Italia", equating New York (a city) and California (a state) respectively would seem plausible.
However, JesseGaronP's post states: "Non-Latin names do not take declension on Duolingo. York can be translated to Latin because York (Eboracum) was an important city in the Roman empire. (The emperor Constantine was proclaimed emperor there.) California is named after a fictional island which appeared in a novel by Garci Rodríguez de Montalvo. "