In Spanish-speaking countries, the calendar begins on Monday. This means that the week starts on Monday and ends on Sunday.
I can answer you the same thing: why does your calendar start with Sunday? You start your week on Monday, right? You go to your job on Monday, not Sunday. So it doesn't make any sense that your week calendar starts on Sunday.
monday
Monday (lunes) precedes Tuesday (martes) in the Spanish calendar.
The US standard of Sunday as the first day of the week is not observed in much of Europe, with Monday (lunes) often the first day of the calendar week. This is also the ISO standard 8601.
The French consider the week to start on Monday, but this is simply a calendar convention just as the American week starting on Sunday is a calendar convention. It does not change any dates or the work-week (which is still Monday-Friday).
"Calendar" in Spanish is "calendario."
Calendar, in Spanish, is "calendario".
The US standard of Sunday as the first day of the week is not observed in much of Europe, with Monday (lunes) often the first day of the calendar week.
The French week starts on Monday (lundi) and ends on Sunday (dimanche).
Both the English and Spanish calendars follow the Gregorian calendar, which consists of 12 months with varying numbers of days. They both start the week on Sunday and have seven days in a week. Additionally, both calendars have common holidays such as New Year's Day, Christmas, and Easter.
Because most Spanish-speaking countries are predominately Roman Catholic, and the Roman Catholic church teaches that the Sabbath is Sunday. But the Bible says the Sabbath is the seventh day. So in order to make Sunday the seventh day they start the calendars with Monday. So, why is Saturday in Spanish a cognate for Sabath? It is called Sabado.