Grishka, In this document they say he learned it with his nurse, so I suppose it was well before he was 12.

If you wonder what it means in this sentence "Cette chanson d'Estelle constitue un exemple unique de la langue provençale provençalisant." I take it to mean that it's an example of a Provençal work in Provençal, not just mentioning it was in Provençal but written in French.

No, the language of the poem isn't archaic at all, someone could have written in nowadays. The language hasn't changed much in the last 400-450 years (check the Provençal carols). It isn't more literary either, it's everyday life Oc. I agree that the Provençal version is more likely to be the original one: the French version sounds more affected but it was written 250 years ago so they might have felt differently from what I may feel now; besides he needed to make the lines rhyme. Anyway, if he'd written the French first, the Provençal wouldn't sound so "easy going".