this is just my 2 cents as a silly cat on the interwebs:

artificial languages designed to be international ones always feel a little authoritarian to me, as people usually arent going to want to learn something that isnt useful or fun to them, so youre at a disadvantage going that route, as you fail to pick up the population required for a common language. to make if work, you need to lower barriers to learning languages, while also providing a motivation to learn it, and for a new conlang, that initial growth is the hardest part, from what ive seen.

as for using an LLM to create a mix of eng+esp, that really doesnt scale much past the americas imo in terms of speaking population, what about Hindi or Mandarin as an example? not to mention the issues with LLMs in general on the environment. as far as i know there really isnt a way to make a conlang that fits in all compatible aspects for all the world's languages, and honestly, i dont think that's a bad thing. languages are fun and beautiful when they are unique, though it does stifle communication between people.

i think youre headed down the wrong path here, there is no (single) language of solarpunk, and i think there shouldn't be. to me, solarpunk has always been about the people, and people speak different languages, have different dialects or accents, or maybe cant speak at all. to me, what you described was the language of solarpunk, overcoming challenges in communication for the benefit of all. in my solarpunk vision, there are many languages in a community, and most people can speak a few, and sign at least partially if they can,while translators and language education is publicly funded (whether though coops or a government). solarpunk needs translators, not dictators telling them how to speak (side eyeing the french govt here). imho international languages font work within the moral framework of solarpunk, you need either colonialism or globalism to spread a language far enough to become a common language, im not sure how youd acheive it otherwise.

anywho, i only dabble in a little bit of conlangs myself, so i may have missed something xx meow