A brief addition to my point about linguisto-cultural differences
I stress that the considerable number of languages were, including the intra-group (for want of a better term, not being a linguist, but "social" languages used to different people within a group, such as older people, aunts, uncles, parents etc. etc.) languages were quite separate languages, not variations on the one language.
So, one person, especially a child, may speak anything up to eight languages every day, fluently and naturally, depending on to whom they spoke.
Further, while there were considerable similarities across each language group's religion and social customs, there were also considerable differences.
Thus, to refer to First Australians as one group, or their spiritual beliefs as one religion would be like referring to everyone in Europe in 1788 as a single group, or christianity as a single religion, when in fact, despite great similarities, it's full of different practises among different language groups in different areas.
So, one person, especially a child, may speak anything up to eight languages every day, fluently and naturally, depending on to whom they spoke.
Further, while there were considerable similarities across each language group's religion and social customs, there were also considerable differences.
Thus, to refer to First Australians as one group, or their spiritual beliefs as one religion would be like referring to everyone in Europe in 1788 as a single group, or christianity as a single religion, when in fact, despite great similarities, it's full of different practises among different language groups in different areas.