Maybe I should also mention that Dave Gorman, as is his name, got it right in Portuguese also.
Because, in Portuguese, Monday is not called Monday. In Portuguese the days are named as follows, literally translated:
Monday - Second
Tuesday - Third
Wednesday - Fourth
Thursday - Fifth
Friday: Sixth (Sexta)
And so, the first day must be Sunday; Domingo, and the seventh day Sábato.
That's as far as my Portuguese goes.
Just because coincidences are not coincidental. When I was in Portugal, at a lake for cooling, there was an abandoned TV magazine lying there, and I started to read it. It turned out to be a puzzle. Segundo? What do they mean second??? ... Next day... Terzo... Say what? Terzo... How does this work???
It took me half an hour to figure that out.
And then, recently, I vaguely remembered that my father mentioned it once. He went on vacations to Portugal, and once he mentioned that, in Portugal, the days don't have names but numbers.