I tried "That is not your business.", and it was accepted, with the alternate answer given "That is not your thing.". It seems to me that those mean two entirely different things though, with "…business" meaning that someone is being nosy, and "…thing" meaning that is either not good at something, or not interested in it, or both.
Does "…afero" really have both of these meanings in Esperanto?
This is, IMHO, one of the Great Weaknesses of the Duolingo format. It's set up in such a way that course authors basically have to include a large number of "alternate translations" - and if the array of translations is too narrow (or even just seen as too narrow) people will complain about it, and bad translations are added. (NB, I have not - yet - said whether I think this one is a bad translation.) As an example, several sentences allow "cloths" [tukoj] as a valid translation of "vestajxoj" [clothes] simply to keep from frustrating learners who don't remember how to spell "clothes."
In this case, the best translation really is "that is not your business." However, since in other contexts "afero" would be best translated as "thing", the course authors more or less have to accept "that is not your thing" regardless of whether it's a good translation.
So, to the obvious question that I have been avoiding so far: "Is it a good translation" - I will say this. Yes, I can imagine a context in which you might have a thing and I might have a thing and I say "this is your thing, and that is not your thing" - but that context seems awfully contrived to me - so, I suppose, the course needs to accept both translations, but if you ask a human (and not a software program) the answer is that it really means "that is not your business."
The course creators need to input every single correct sentence into the system, and you can't blame them for not wanting to waste time thinking about every single possible answer and word permutation when they wanted to finish the whole product.
Helping them get those meanings right is our (the community's) job now, by reporting answers as correct and later seeing them corrected (that's why it's called a beta version - all inputs are welcome).
Since english is not my language, i cannot explain it myself, but here is a link that you may find helpful: http://fr.lernu.net/komunikado/forumo/temo.php?t=1289 The second and fifth posts are good explanations.
Tion is just the accusative case of tio: "mi sxatas tion" : il like that (this is an exemple i made myself, therefore, it may be wrong. Wait for someone to correct it). You can do the same with Tiu.
If it answers questions like "What is that" -> "Kio estas tio", you use "tio": "Tio estas pomo" -> "That is an apple".
If it answers questions like "Which apple is bigger" -> "Kiu pomo esta pli granda" you use "tiu": "Tiu pomo estas pli granda" -> "That apple is bigger".
If it answers questions like "Who is that" -> "Kiu estas tiu (persono)" you also use "tiu": "That (person) is the doctor" -> "Tiu (persono) estas la kuracisto".
Notice that "tiu" always have a noun after it, either mensioned or implied, whereas "tio" (usually) stands alone.
Why is afero such an ambiguous word in Esperanto, meaning thing, affair, business, matter, case, issue. Did it always mean all these things, or has it been anglified?
Saying "that is not your thing" means something completely different to "that is not your business". or "that is not your issue" or "... case"
I don't understand your thought process for using "anglified" here. If anything, it seems the opposite is true.
I wonder, though, whether some of the other discussion in this thread might answer your question. I'm thinking particularly the question from laVeturigisto and my reply talking about the Great Weakness of Duolingo - although several of the shorter posts kind of make the same point.
Thanks. The other thread did explain it rather well. It just seemed the word had too many meanings, but then again, one of the reasons it might do is because English has different words that, when their meanings overlap, one word might be called for in Esperanto, and that isn’t the same as would be used for other meanings of those same words in English, and suddenly the dictionary has to list a whole range of words as possible translations for one word in Esperanto.
It’s the eternal conundrum of the impossible one-to-one translation. Let’s call it the dictionary paradox. It’s also why Google Translate always comes up with ridiculously incorrect translations even with just a few words to translate.
Also, as I indeed have seen in many other sentences on Duolingo, some translations are accepted because lack of further context makes them possible, even if not particularly plausible.