Complex sentence: Awabakal was studied by Reverend Lancelot Edward Threlkeld from 1825 until his death in 1859, assisted by Biraban, the tribal leader.
Split into simpler sentences: Awabakal was studied by Reverend Lancelot Edward Threlkeld from 1825 until his death in 1859. The speaker of Awabakal that taught him about the language was Biraban, the tribal leader.