After William Boychuk, a Canadian, was convicted of murder in North Carolina, he was allowed to serve his life sentence in Canada.
Now the New Zealand mosque terrorist has been sentenced to life without parole (an unprecedented sentence according to the article linked below) and New Zealand's foreign minister Winston Peters says he wants him to serve his sentence in Australia since that's where he's from. The Australian prime minister Scott Morrison said that would not be a normal practice, and NZ prime minister Jacinda Ardern said "[T]here isn't a legal basis for it. It would be a very complex undertaking."
How widespread is such a practice? Is this a unique treaty between the U.S. and Canada, or something done everywhere except that it's unheard of in Australia and New Zealand, or something between those extremes?