Kwicky is diverging a bit
in 1970s a non starting initial teaching alphabet was intoduced and dropped around tenyears later when it was shown not to work (kids didnt read faster or better)
This is a huge subject - try The Language Instinct by Stephen Pinker, I think
The country with the most profuse language differences is PNG (papua new guinea) and so any book with linguistics and PNG in the title is going to look at the profusion of languages. I think they talk of classes, stocks and orders of languages and PNG has the largest number of language stocks.
so, if there was this diversity of languages, well everywhere, then why does English, Arabic and Mandarin and Spansih account for at least 50% of speakers of any language ? This is a question in historical or geographical linguistics
what else ?
Oh yeah.... you need to look at anatomy and decide how the human larynx developed
as that is necessary for forming sounds that we do that chimps can't (big effort in the fifties trying to get chimps to speak and understand, and then teaching them sign-language and then giving up as a waste of time - see First signs of washoe)
you can spend years on this......
PP