Wow! Glad there are scholars who can figure these things out. Wish I had that kind of academic fortitude.
Cracking cuneiform seems like a terrifically difficult accomplishment, and I really still think it was, much worse than Egyptian hieroglyphs.
A large archive was excavated. None of it could be read, but the patterns of signs made it possible to discern that a number of languages were recorded using the same writing system.
Two languages comprised the bulk of the archive.
The first one to succumb was Akkadian. As an extinct Semitic language, it had living relatives and familiar structures. After it was cracked, it was realized that the little stylized pictures used for the characters didn’t work as mnemonics of the word/sound that is found in Akkadian.
However, this development meant that even inscriptions in unknown languages could be pronounced and read aloud. It became clear that the other large collection of one language was the original for which cuneiform was devised — Sumerian. Sumerian is a language isolate, had and has no known related tongues. Its agglutinative structure was discerned.
The late Samuel Noah Cramer notes in his general reader book on the Sumerians that the rivers and even the cities in which they lived had non-Sumerian names, and that these names are likely to be loanwords from the earlier inhabitants who spoke one or more unknown and vanished languages.
The Sumerians didn’t say much about their origins, apart from the idea that their first presence in Mesopotamia was a known city on the shore of what’s now the Persian Gulf; they called themselves “the black-headed people”; they were skilled with numbers, but each city-state used a different system to write them.
https://search.brave.com/search?q=who+cracked+cuneiform&summary=1