What is the origin of yakka?

Yakka “work” is a term in Australian slang that used to be spelled variously as yacker or yakker, among other options. Because Australian English is a variety of English that is non-rhotic, dropping the r sound after a vowel, the original spelling of yakka may have changed to reflect this r-dropping tendency. While the ultimate source of yakka is obscure, the most popular hypothesis is a derivation from yaga “to work,” a word from the Yagara language. Yagara, also known as Turrbal, is a language native to Queensland, the northeasternmost state of Australia, and belongs to the Pama–Nyungan language family, as do three-quarters of all aboriginal languages of Australia. Yakka was first recorded in English in the late 1880s.