I am learning Breton (le breton) and capitalization is clearly different in French (le français) and English (l'anglais).
I wanted to buy a book so I went to https://www.pourlesnuls.fr/. There I could buy
All the capitalization seemed to agree with the standard rules for French titles as I understand them:
the first noun is capitalized
any preceding adjective is capitalized
everything else follows standard French rules
so why are languages not capitalized when they are the first noun of the title?