> There are some cognitive scientists who believe that the ability to use language is built into the human brain, and (natural) language acquisition basically involves just setting the "parameters" of that built-in system.

This, by the way, is essentially what Chomsky means by “universal grammar,” in his writing - the inborn language capability and its fundamental structure. His theoretical framework even went through a period where it was called Principles and Parameters.

As someone who tinkers with conlangs as a hobby and has been working on a similarly highly-engineered language not unlike ithkuil in features, this is one of the main things I struggle with.

Actual natural language is very fluid. Spelling, pronunciation, grammar, all shift around, and for all manner of reasons. But the main one is efficiency. Humans are always subconsciously trying to cram as much information into as little time as possible, while preserving enough intent. This means extra redundant information whittles away, but there has to be enough redundancy for error correction.

With these highly compressed languages, the problem becomes that a slight mispronounciation or misspelling can totally mess with the meaning in ways which lead to confusion. There are just too many phonemic sounds (a given sound difference is phonemic if the distinction matters, eg in English, p and p' (aspiration) is non-phonemic, but in Korean it is)

When you actually analyze languages for their "baud rate" so to speak, languages with more symbol diversity (English) have less phonemes per unit time, while languages with less symbol diversity (Italian) have more phonemes, but the overall entropy per unit time works out pretty much the same. (I can't find my exact source right now, but if you poke around keywords like spoken language entropy rate, there's quite a bunch).

Basically when you have machine code as a language, you pretty much need machine brain to process it.

Edit: here's a start of some sources:

https://seantrott.github.io/information/

Which mostly cites https://www.science.org/doi/10.1126/sciadv.aaw2594

Where would you say Esperanto sits on the "natural" scale, since it's design goal is to be easy to learn and use as opposed to being highly compressed? As I wouldn't say its "[s]pelling, pronunciation, grammar, all shift around, and for all manner of reasons".

Many children have acquired Esperanto naturally, as a first language, and that does seem to work without any problems.

That seems like a very dangerous experiment to conduct on a child.

How? Did you think they meant only language?

> has evolved to be compatible with our brain's language mechanism.

Under the hypothesis that there actually is such a "language mechanism": There would be a host of other mechanisms a language needs to compatible with - such as spoken and written word - that might have contributed adversarial constraints along the way (from the perspective of optimal adjustment of a language with respect to this mechanism).

There’s a whole strand of work in phonology (and other linguistics areas) called optimality theory, and the basic idea is that what you see in surface-level language is the the result of solving a competing constraints problem.

> which I believe might be the main reason why all conlangs from the past 100 years have failed to reach widespread adoption

Given how much people hate learning much more basic things—new programming languages, new operating systems, new tools—it seems hard to come to any conclusion about conlangs based on popularity! Languages are hard to learn, have immense cultural significance and are dominated by network effects. The potential advantages of a constructed language are, at best, illegible. What would push anybody to learn a brand new language well enough to actually use it?

Whether or not a language becomes popular tells us little to nothing about the language itself.

Generative grammar is extremely nativist. The truth is, people will learn anything society forces them to learn. In Piraha society nobody is forced to learn recursion and consequently nobody thinks recursively or in numbers.

The global languages of A.D. 2023 (English, French, etc...) are probably stuck in a similar "Chomsky tarpit" as Piraha, but because we're so globalized and together nobody is brave enough to look out of this tarpit.

I am constructing a conlang codename LXX (because it has 70 phonemes, 15 vowels and 55 consonants, but they were carefully chosen to be learnable to pronounce unlike Ithkuil) for the purpose of getting at least one human society out of this tarpit.

The new 2023 ithkuil addresses this with only 32 consonants and 9 vowels