Can I gift my friend in Australia a Xbox live subscription?

You would have to find a retailer where you could purchase a code for their region.

Xbox gifting is region locked, which it would have told your friend before he sent the gift, so there's no way to redeem the code unless you're in Australia also. Your friend would need to see if he can submit a refund request for the purchase.

I also received a gift from a friend. I live in Brazil, and my friend in USA. I can not redeem my gifts.

Hi. I live in Australia and I have a friend from the US who wants to send me a $5 USD Gift card. I was wondering if it is still possible to redeem it and if it will be automatically turned into AUD or if that's not possible. Thank you

No, gift cards need to be done in region. You could move your location region to the US and use the giftcard then. but you can not cross region use gift cards.

Basically when someone is buying a gift for someone else through the console or online a box will popup before finishing the transaction that says that this gift will ONLY be able to be used in the region that it is purchased in. For instance say I have
a friend in Australia that wants to gift me (I live in the US) a game he would not be able to do that because we live in two different regions. Hence this is where this error you are getting is coming from there is no way around it the only thing that we can
recommend is to have whoever gifted you this game is to have them contact xbox support by going to support.xbox.com/contact-us and see if they can get a refund.