In Austria, there is a gifted gentleman named Georg Fischer, who is truly devoted to Guru Rinpoche, and who has invested many years to the study of dakini language, as revealed in terma scrolls.
In this world, there is nobody quite like Mr. Fischer. Note to alert editors and publishers: a book by this gentleman is a smart idea.
I would urge you to visit his site, Dakiniscripts, and his related site on Lantsha. These are very valuable resources, unique in every way, and may be regarded as authoritative.