Duolingo usually insists on literal translations, unless those are unnatural. So:
- I do not want to sleep = Я не хочу спать
- I do not want sleep = *Я не хочу сна (although this sounds unnatural in Russian, not sure about English)
What's the difference between "я не хочу спать" and "я не хочу поспать"?
"Я не хочу поспать" means I don't want to take a nap. Adding the prefix по- changes the aspect (in this instance) to mean "for a short time," in other words, to take a nap. However, you will probably not hear this often, since the progressive aspect is usually more appropriate.
See JohnNatter1's comment below for more nuance.
http://chehov.niv.ru/chehov/text/spat-hochetsya.htm [СПАТЬ ХОЧЕТСЯ] This story of Chekhov is always titled "sleepy" in translations. "I am not sleepy" should count as a correct translation.
Both хочу and сплю are personal verb form.
In Russian, only the main verb in the sentence has the personal verb form, and other verbs are put into a special verb form, infinitive. Here, хочу is the main verb, and спать is subordinated to it, so спать is put into the infinitive: Я хочу спать.
(Not all Slavic languages are like this. For example, Bulgarian doesn’t have infinitive and uses personal verb forms in its place.)
спать (spatʹ) [spatʲ] impf (perfective поспа́ть) "to sleep" From Proto-Slavic sъpati, from Proto-Indo-European swep- (“to sleep”). Cognates include Russian сон (son, "dream; sleep"), obsolete English asweve (“to put to sleep, to stupefy”) and sweven ("a dream; a vision"), Norwegian sove ("to sleep"), Lithuanian sãpnas ("dream"), Ancient Greek ὕπνος (húpnos, "sleep", whence English hypnosis), Latin somnus ("sleep", whence English somnolent) and sopor, Spanish sueño "sleepiness; sleep", Irish suan, Persian خواب (xvāb, “dream”), Sanskrit स्वप्न (svapna, "sleep; dream") and स्वपिति (svápiti, “to sleep”).
In "I don't want to sleep", "sleep" is being used as a verb. If you say "I don't want sleep" then you'd need to use the noun "сон" appropriately declined: https://en.wiktionary.org/wiki/%D1%81%D0%BE%D0%BD#Russian .
Your sentence, which I think should be "Я не хочу сплю́" BTW, means, "I don't want I sleep".
I put in "I don't want sleep", why is that incorrect? I mean, I know it's not used as a noun here, but it still makes sense in English.
I mean, it really doesn't matter, but it's odd that duo doesn't accept it. I've seen stranger versions that duo accepts. (different sentences, where the meaning is essentially the same, but the words themselves are quite different)
"I don't want sleep," is grammatically correct, but it is not something a native-born American would say in an everyday situation. "Я не хочу спать," on the other hand IS something a Russian would say in an everyday situation.
In reality, "I don't want to sleep," is also unusual. You are more likely to hear, "I'm not tired," or, "I don't want to go to bed. It's all about context.
Incidentally, Americans are likely to say, "I need sleep," or "I need some sleep." The register is casual conversation.
You will also hear them say, "I need a nap," and especially (to or about their young children), "You need a nap," or, "Someone needs a nap," where "someone" means the child in the room.