Doctor Zamenhof was inspired by his (native?) Polish czy when creating this word. It is also a question particle.
I thought "Ĉu ne?" meant "Isn't it?" and "Ĉu?" meant "Really?", but I see your way of thinking. In a question it seems to mean "Is this true?" at the beginning of a statement that you can answer yes or no to. I think it is kind of similar to the French question beginning "Est-ce que ..." which cannot be literally translated to English ("Is it that..."), but gives the same feeling. ("He plays." becomes "Does he play?" We could say "Is it true that he plays?" or "Does he really play?") See the tips and notes for this lesson and scroll all the way down: https://www.duolingo.com/skill/eo/Basics-2
That's a lot of languages Duolingo offers to learn. I spend an enormous amount of time, more on some than on others. Of course, it makes perfect sense to learn Esperanto, as it will be impossible to learn every language there is. Sign Language and Braille are the other two essential languages, as I cannot expect a deaf person to listen to me speak or blind person to write to me in English.
"Ne" means "not" as well as "no" http://esperanto-panorama.net/vortaro/eoen.htm http://www.gutenberg.org/files/16967/16967-h/16967-h.htm#letterC
"Ĉu ne" means "Is it not?" or "Isn't it?" which is simply a contracted form of the same thing.
This expression doesn't really translate word for word. We replace their expression with one of ours. We could say "He plays, is it not so?" or "He plays, doesn't he?" or "He plays, or not?"
I think this is similar to "acha(s) " in portuguese or "you think..." in english. In portuguese, using this word is kinda optional but it lets the other person know that a question id coming and a feedback is expected. In portuguese, not using a word like this still makes sense but in esperanto things dont seem to "flow" right without it.
Having said, I think thus exercice is not not only wrong but it is also not very friendly for begginers. The next exercice clarifies more the use for this word.
"Eh?" in the US is more like "What did you say?", "Excuse me, could you repeat that?" or "Huh?", "I didn't get that. What?"
"Is it so?" or "Really?" is more like "I heard you, but I am not sure that I believe you.", "You have got to be pulling my leg.", "Are you sure you're not just trying to pull one over on me?", "Are you just kidding?" although it could be "I don't think so. Are you sure?"
Unless you are Canadian, in which case you might just use it for this also. Even then, it is different as it is used for both "Isn't it?" and "Is it so?" It is also used here and there just to see if people are paying attention, as in "Did you get that?", "Did you hear me?", "Are you even still listening to what I am telling you?" You yourself called it a conversational word making me immediately think of this last Canadian use, which is not the same as "Really?" or "Is it so?" : "I was going to the store, eh, when a big truck crashed into the gas station, eh and you should have seen......" Here it is used more like "This is exactly what happened. There is no doubt, but are you listening? Wait until you hear what happened next?"
"Isn't it?" is more like "I thought it was so. Am I wrong?" or "This is the way it is, but perhaps that is not true?"
"It's nice here, eh?" but is it used this way by itself? We would certainly assume the first meaning when it is by itself.
The Jamaican pronunciation of 'true' is 'chu' because tr slurs into ch. But even they would say 'fi chu' what they write as 'for true' or 'a chu' meaning 'is it true'. Its intresting how. Esperanto has so many similarities with creoles, except for being easy to pronounce, and compensating grammatical simplification by being rich in modalities.
I think that is because it is a stand alone word here. "He plays, right?" could work, but "Right?" is certainly not used much whereas "Really?" works better alone. Like a dictionary, we need to pick the best definition for the situation or sentence. Not all definitions apply to all sentences.
So, you use "Right?" all by itself? I would definitely not, but I would use it at the end of a question. You could try reporting it and see whether Duolingo will add it as an alternative, or not. I personally think it can be used for this word when not used alone, which is why it is listed.
"if" is listed as "se"
"whether" does list as "Ĉu"
http://www.gutenberg.org/files/16967/16967-h/16967-h.htm (English to Esperanto)
However in this dictionary, which goes from Esperanto to English, more meanings are listed: http://esperanto-panorama.net/vortaro/eoen.htm
"ĉu" is listed as "either", "if", "is it", "whether"
I think an alternate for the stand alone which Duolingo has as "Really?" could be "Is it so?"
"Ĉu" is word which makes thing interrogative. 'It is a book' - 'Gxis estas libro', 'Is it a book?'-"Ĉu ĝi estas libro?", By alone 'Ĉu' is itself a question 'weather it's real or not'? 'really' is not exact translation but equivalent or approximate. Real translation for 'really' in Esperanto is 'Vere'.
'Ĉu' may seem odd but such words are exists in other languages. For example, in Hindi word 'kyaa' works exactly like 'Ĉu' .
'Yes kitab hai' - 'Ĝis estas libro', 'Kyaa yeh kitab hai?'-"Ĉu ĝi estas libro?"
Ĉu? - Kyaa? (Kyaa, sach me?) = really?
Ĉu is a question participle. Literally it means "whether", so in this context it means "really", as you could take it as a "please reaffirm whatever you just said" or "could you explain more about that?" if used alone. It's definitely a nuanced word.
"Vere" (literally "truly" from vero, "truth") is used often to mean "really". There's also "reale" (literally "really" from realo, "reality"). These are often interchanged, with "vere" being more common due to its shorter pronunciation, but I feel like there are some situations where you should use one over the other.
A) Mi havas dek katojn. - I have ten cats.
B) Ĉu?! - Really?!, Are you kidding?!
A) Mi ricevis malbonan noton. - I got(received) a bad grade.
B) Vere? - Really?, Truly?, Are you speaking the truth?
A) Estas monstro sub mia lito. - There's a monster under my bed.
B) Reale? - Really?, In reality?
Really? is the correct answer, cause if you see the prounouce (plus sorry for my grammar :c) that with cap letter at beginning (example: Then), then its the right answer. Its easily to cheating (for me thought) except if there is two with cap letter. Hope its help for beginners.
I've always interpreted Cxu as a word representing a binary query with implied options. So the way I've been think of this is "Is that so?" It implied that the query implied to the previous statement. The thing that confuses me though is when the course says "Ĉu la bebo estas knabo aŭ knabino?" Following what I thought was the definition, the answer to this question should simply always be "Jes." since the baby IS a boy or a girl. That would be an abridged for of "Is it a boy or a girl?" then "Yes, it is a boy or a girl."