The guide below will let you people help to change Siri language on iPhone according to your requirement. Incase someone else who uses your iPhone have changed Siri language, but you only understands English then no need to worry simply follow steps below to reset Siri language easily.
Change Siri Language on iPhone and iPad
Go to “Settings” > “General”
Tap on “Siri”
Tap “Language” and select “English (Australia)” from the list and thats it
To experience, tap on Siri button and see the language is changed now.