Some countries do adopt weeks starting in Monday, whereas the weekend (Saturday followed by Sunday) is at the end of the week, making Sunday the seventh day.
In Brazil, where I am from, weeks start at Sunday and, since working days (monday-friday) are called as ordinary numbers (segunda-feira/second 'feria' (latim)/monday, etc), it would not make sense to adopt a week starting in monday (since monday is called 'second').
However it only exists in Portuguese speaking countries (correct me if I am wrong). In many countries, weeks start in monday and it makes perfect sense for them.
Trying to explain what Sabbath is to a Christian friend from Indonesia (I am Seventh-Day Adventist), I wasn't understood when I said that Sabbath is celebrated on Saturday, the seventh day. "But the seventh day is Sunday", I heard.
How does Sabbath get celebrated on countries where week starts in Monday? How to explain Sabbath as seventh day to someone from these countries?