ML over historical languages is no different from ML over currently spoken (and written) languages, with one crucial exception: if the language is still in use,

ML over historical languages is no different from ML over currently spoken (and written) languages, with one crucial exception: if the language is still in use, you can get a bigger corpus. About dictionary making: there are several programs "out there" that are already set up for making dictionaries, probably better than going from scratch with YAML. SIL's FLEx is very good; their older Shoebox program is also useable, but like the C programming language, you can shoot yourself in the foot. There's another one out of East Africa, but I can't remember its name. I don't know much about Australian languages, but I think most of them have a lot of morphology. If yours does, then you'll want to do something about inflected forms of words (think English walk, walks, walked, walking); you probably don't want to store all of those forms in your dictionary, instead you'll want to choose a base form from which the others can be derived. Again, tools like FLEx allow you to create morphological parsers that help with that. Finally, I'd suggest that if you haven't already done so, you should take some courses in linguistics. It will make it much easier to reason about your lexicon, the language's grammar (syntax and morphology), and so forth.