Where does “Australie” come from?

Australie (French) comes from Latin australis, from Latin auster, from Proto-Italic *austeros.

Ancestry of “Australie”, step by step

Step	Language	Word	Meaning
1	Latin	australis	southern; Australian; the south pole
2	Latin	auster	The south wind; south
3	Proto-Italic	*austeros	—