3Blue1Brown's (Grant Sanderson's) YouTube series on linear algebra does a phenomenal job of developing the intuition needed to understand the topic.
 

I was delighted to run across this post; I joined lesswrong so that I could reply to it!

There have been some pivotal changes since the push was made to adopt Esperanto as an IAL; perhaps the idea should be explored again.

One of these changes is AI.  It should soon be possible to make an "AI friend" -- basically a glorified tablet, perhaps with a simple arm - that could serve as a baby monitor and speak to the infant in the IAL.  The child would learn to speak the language effortlessly if it is well-designed and completely regular.  The AI friend could also teach the child to read the language, as well as some arithmetic, colors, animals, measurements, etc.

This would greatly reduce the enormous costs of teaching children an IAL in school, while doing a better job of it.  One of the problems with Esperanto back in the day was that even if we had succeeded in teaching every kid in the world Esperanto, it would have been spoken a bit differently in each country, and there would have been further drift from there.  But every child learning an IAL at a young age from an AI friend has the same teacher, eliminating regional differences and drift.

Such a dramatic reduction in cost changes the calculus.  Another change to the calculus is provided by climate change and the low birth rates in many countries, both of which will stimulate massive immigration.  Immigration is vastly more difficult if the immigrants do not speak the host country's language; the costs are enormous.  For one thing, immigrants often are less economically productive because of the language barrier, so they are poorer, and they pay less taxes to the host country.  (As an example, I know a surgical nurse who is immigrating to the US but will likely clean toilets with her mother because she is having a hard time learning English.) When we are talking about tens or hundreds of millions of immigrants, the costs of such reduced economic productivity are enormous.

Moreover, immigrants who don't speak the host language tend to live in enclaves rather than assimilating into the larger society.  There are many such Spanish-speaking enclaves in the US.  This too has consequences.

I'd love to chat more about this; I have written privately about the costs of teaching the world's children hundreds of different natural languages and then dealing with the difficulties that causes, but am looking to engage with others with the same desire to see the world learn a common language.