Kinds of reminds me of the different registers of Javanese, only way more restricted in its use (only with in-laws and a few cousins? Wow!).

So how--when it was in regular use--did one learn Jalnguy? Who would teach it to you?

Dixon's article on Dyirbal 'mother-in-law' language was one of the seminal influences in my early linguistic training. The Jalnguy vocabulary was a reduced set, in effect a set of somewhat more abstract semantic primes in a one-to-many relation with normal vocabulary. Sort of like the abstract labels the Coneheads (later) used to denote the strange items they encountered on Earth.

That introductory class on semantics was followed by another that focused on a Papuan language, Kalam, whose verbs were almost nothing but semantic primes. Even words like 'see', 'hear', 'smell', etc. are composite: 'eye-perceive', 'ear-perceive', 'nose-perceive', etc. 'Perceive' is replaced by something more agentive to render the equivalent of 'look', 'listen', 'sniff', etc. Australian Jalnguy and Papuan Kalam gave me a wonderful feel for compositional semantics, although I was never that much of a fan of the mechanics of generative semantics, which was in brief flower in those days.

Stuff like this just makes you want to drop everything and go into anthropological linguistics.