I think it's a question that's been brought forward by anthropologists and ethnologists. I spent 23 years at the UN, negotiating the UN Declaration on the Rights of Indigenous Peoples, and whenever we were meeting with the Canadian delegation and did not want them to understand us, my brother from Alberta—Wilton Littlechild, who is Cree—and I would speak in Cree. He would perfectly understand what I was saying and I would perfectly understand what he was saying. He supposedly speaks Plains Cree, but there is not much difference.
On March 20th, 2018. See this statement in context.