As Australia is an English-speaking country, you can say it just like in any other english-speaking country...
However, not many Australians call it a restroom, but simply refer to it as the toilet.
A bathroom is a bathroom. It contains a bath and/or shower, wash basin and vanity, and whatever other trappings there may be of a bathroom. If there happens to be a toilet in there, it is still called the bathroom. However, most Australian homes do not have a toilet within the bathroom, except for in the ensuite.
The small room containing the toilet is simply called the toilet. It is also colloquially known as the dunny.
Where is the bathroom? it is as simple as that, we are not from a different world where everything is country-style in the outback.
bathroom
To say 'He is going to the bathroom' you would say 'Va al baño.'
Bathroom is "badkamer" in Dutch.
weh di bathroom deh?
'I lost my cat in the library bathroom"
'Bathroom' in Spanish is 'bano' (there is a tilde above the 'n').
tenedre
toilet
Badezimmer
tyanet
The Romanian language equivalent of where is the bathroom is unde este baia.
To say "With shower" in Yoruba, you would say "Pelẹsẹ kan wipé nṣiṣẹ." To say "With bathroom" in Yoruba, you would say "Pelẹsẹ kan wipé ìtẹnu."