[k8si]

Communication rates are very similar across languages: https://www.science.org/doi/10.1126/sciadv.aaw2594

See also (great read): https://pubmed.ncbi.nlm.nih.gov/31006626/

wrt your Spanish example: grammatical gender adds information redundancy to make it easier to process spoken language (e.g. helps with reference resolution). This redundancy enables Spanish speakers to speak at a relatively fast rate without incurring perception errors. English has fewer words but a slower speech rate. It's an optimization problem.

The speech rate issue isn't as obvious if you're only looking at text, but I'd argue/speculate that lossless speech as a language evolutionary constraint has implications for learnability.

tl;dr there is no communication tax, languages are basically equivalent wrt to information rate, they just solved the optimization problem of compactness vs speech rate differently