Looking at https://en.wikipedia.org/wiki/Names_of_the_days_of_the_week#Numbered_days_of_the_week https://en.wikipedia.org/wiki/Names_of_the_days_of_the_week#...

Looking at https://en.wikipedia.org/wiki/Names_of_the_days_of_the_week#Numbered_days_of_the_week https://en.wikipedia.org/wiki/Names_of_the_days_of_the_week#..., it appears that almost every language which numbers the days of the week starts on Sunday, with the exception of some Slavic languages (which use Monday) and Swahili (which uses Saturday).