Yes, I think Portuguese, and I guess I don't know that accent well, but it didn't seem consistent, whatever it was. But yes, I did kind of settle into the performance eventually, and I think a second viewing would be even better, now that I know what to expect.
I really liked the choice, too, that Driver's character was just gone - and then suddenly introduced again, in a very extreme state of being, and we don't know what, exactly, he's been through nor everything that was personally or emotionally involved in that final action of his. I like the not knowing there as it mirrors the perspective of the final narrator of the film, who is observing the priests and has no idea what they've been through and cannot really judge what is in their hearts.
Curious about that ranking, too. I suspect it'll take a few years for its placement and for opinions to settle.