English usage and grammar

You bettern't.

Just try it with "not". If it does not (doesn't) work, then you probably should not (shouldn't) do it. There isn't a hard and fast rule on the use linguistically speaking beyond that.

I read not manga. I grow not potatoes. That sounds not like a good idea.

None of these really work, despite getting the idea across.

Speaking a language is more about the idea you're expressing and there is a lot of space in there to be a bit weird. That doesn't mean to just throw away currently established rules and expectations unless you're just trying to be silly and misunderstood. It's just not a very effective or efficient way to speak.

"Need" and "dare" are auxiliary verbs for some speakers. That's what allows them to bypass the "do-support rule" for those speakers.

On the other hand "read", "grow", "sound" are not auxiliaries, so they require do-support in this sort of negation.

For correctness, it only works with a few words like you mentioned, and in specific circumstances.

Playfully or in old form speech that people don't commonly use any more, people can expand it to a few other words.
You have to be able to replace the "n't" with "not", and you wouldn't say "no, I read not them".

Other replies explained the technical rules better than I, but I thought a less technical answer might be appreciated.

If you're being playful, you could say "I read not the mangas", which doesn't sound wrong as "I readn't the mangas". (I don't know why you can't use "them" in this context, but there's definitely a technical reason).
Just be aware that you would come across as archaic and silly, and possibly incomprehensible depending on who you're talking to and their comfort with wordplay.

I'm no linguist but it's all basically unwritten rules and conventions and the examples you gave are wrong in the sense that they break other rules. For example noone asks "read you manga", they say "Do you read manga?" In which case "I don't" is fine, but "I readn't" isn't. In short it can't be done with every verb, and as a native speaker I'm not aware of an explicit rule that governs which verbs can and can't have contractions.

I’m not entirely awake, but it looks to me like it can be added to helping verbs. “Need” isn’t (as far as I remember) a helping verb, but it looks like that’s how it’s functioning in your “needn’t” example.

(Note: “pronoun” in your title is not the right part of speech at all)

Contracted “not” (-n’t) can only apply to auxiliary verbs and main verb “be” (copulas are strange ). Because poetic forms like “She knows not the way” are not ungrammatical to native speakers, I suspect that they were once more commonly used and survive today as art and perhaps some ritual speech. But they were likely not contracted.

Subject-verb inversion for question formation is common among Indo-European languages. In modern English, it’s only done with auxiliaries to form yes/no questions, but again it may have been done with main verbs in the past.

If you’re really interested, check out a good English linguistics course.

I wouldn't've'd thought about this myself honestly.

"I'll partake but she token't."

i get the question, but your examples seem contrived. they're all actually "have"/"did" inquiries.

have you read that manga?

have the potatoes grown?

does it sound like a good idea?

did it sound like a good idea?

if one reads them this way, one can see a clearer connection between these questions and question tags--and the reason why certain verbs in the tags have a tendency to be overused in speech, ultimately leading to necessary contraction.

I think it's customary to only use it with certain verbs, mainly ones that are also helping verbs (do, can, should, will). And all the sentences you use as examples can be rewritten to use do, e.g. "No, I don't read them."

Will becomes won't for its contraction, but you would never hear it used when it's not a helping verb, e.g. "The psychokinetics will the object to move" word never become "The psychokinetics won't the object to move" because that's not where the not word be in the sentence, whereas "The psychokinetic will move the object with her mind" readily is negated to "The psychokinetic won't move..." because that's the normal place for a not in the sentence.

"Need to" is almost a helping verb sometimes when it acts like must, like "I need to wash my hands" -> "I needn't wash my hands" Or the more common "I don't need to wash my hands"