[1] https://tokiponacensus.github.io/results/#how-people-learned...
Whether you really can copyright a language is pretty dubious though, probably not. In the case of Loglan it was not enforceable but Lojban is now far more popular anyway, so it is moot.
As for Toki Pona in practice it is not much of an issue because the free learning material is good enough. The language is very small and not that strictly defined anyway but I get your concern.
sina toki ala e lon, toki pona li pona.
You are knee deep in a cow piss on a remote farm in Nebraska, offline and some library has some version issue with your proprietary licensed language. A trivial solution if it was free language, but now it requires 300 miles trip. You are in Nagorno Karabakh and just spoke to some random stranger about this new funny speak-language but you cannot give him PDF because it's not free. These issues stings very deep because how artificial and easily solvable would they be. Some things must be free otherwise they cannot be used to their full potential. So you stand there, in Nebraska or Nagorno Karabakh and swear - Never again will I use proprietary language. I have nothing agains proprietary software or linguistic books but the language itself must be free.
Helped immensely in getting around! Of course, I had absolutely no comprehension of what things meant, but I could match sounds to signs and avoid eating things I’m allergic to.
How is this different from any proprietary book about a freely-licensed language?
If you're in a remote farm in Nebraska and you only have a copyrighted Esperanto textbook, you can't share it, even though Zamenhof's materials might be public domain.
I fail to see any problem with toki pona here.
Something similar can be argued about Delphi / Object Pascal. Borland's compiler is non-free, but the language can be used with FreePascal. I'm happily using FreePascal on my personal projects and haven't touched Delphi in more than a decade; it's a nice language and there's nothing wrong with it.
Sharing FreePascal is totally OK, just like sharing freely-licensed materials about toki pona.