In many languages the days are numbered, e.g. “First day”, “Second day”, …, “Seventh day”. Speakers of those languages have no question about when the week starts.

en.wikipedia.org/…/Names_of_the_days_of_the_week#…

Notably, the older languages start the week on Sunday. Some of the languages that start the week on Monday can be attributed to mistranslation from the former group. So starting the week on Sunday is historically more correct.

Disclosure: I speak a language that starts the week on Sunday, so I’m biased.