Allow MLO first day of the week = OS first day of the week
MLO uses routines to calculate dates in the current and surrounding weeks. E.g. Due Date optionally displays the day of the current week, and Automatic Formating Rules can use 'weeks' in the Rules. These do not use the first day of the week defined in the OS, but always use Monday as the first day of the week.
Several countries, particularly in the Middle-East use Sunday as the first day of week, and some countries use Saturday. It makes sense for MLO to use the first day of the week defined in the OS it is running on.
Consideration should be given to how MLO operates when synchronising across different platforms if devices are set to use different first days of the week. Dates are fixed, so dates and times should not change, only the week boundary should move and this should be set by the first day of the week defined in the OS that MLO is running on.
It may be argued if this is a bug or feature, nevertheless, MLO currently uses a fixed Monday to Friday week and does not allow the user to change this. For many countries or people wanting to use a different working week this is a major disadvantage.
It is likely to promote the use of MLO in non-western countries (or by people from these countries) if the working week could be changed, and makes MLO more international.