Hard to remember them all :) but two were Australians who spent a few months backpacking in Brazil... one was a German girl who just blew my mind how well she could speak Portuguese. Another was a Swedish man who just casually started helping a group of Brazilians, in Portuguese, to order something in a restaurant... I think there were many other cases over the years but it's not like a keep track of them all, so I can't give more examples that I remember for sure... but enough, as I said, to convince me that it's not very rare.