Rationality requires intelligence, and the kind of intelligence that we use (for communication, progress, FAI, etc.) runs on language.
It seems that the place we should start is optimizing language for intelligence and rationality. One of SIAI's proposals includes using Lojban to interface between humans and an FAI. And of course, I should hope the programming language used to build a FAI would be "rational". But it would seem to me that the human-generated priors, correct epistemic rationality, decision theory, metaethics, etc. all depend on using a language that sufficiently rigorously maps to our territory.
Are "naturally evolved" languages such as English sufficient, with EY-style taboos and neologisms? Or are they sick to the core?
Please forgive and point me towards previous discussion or sequences about this topic.
How are you so sure of all that stuff?
If you specify in more detail which parts of what I wrote you dispute, I can provide a more detailed argument.
As the simplest and most succinct argument against artificial languages with allegedly superior properties, I would make the observation that human languages change with time and ask: what makes you think that your artificial language won't also undergo change, or that the change will not be such that it destroys these superior properties?