It is, but looking at the wikipedia article it appears that more places use Sunday as the first day of the week overall and adoption of Monday as the first day of the week has been picked up by some nations but largely ignored in areas where Sunday is historically the first day.
And yet when one is is communicating to an international audience you use the international standard rather than default to your own unless their is a compelling reason not to.
For example their are plenty of countries that still use imperial units of measurement, yet in any scientific works they will use metric because that is the international standard and in doing so allow scientists around the world to easily reach a common understanding of the data.
Also in science, most languages will have their own words for various animals, but to the same extent when discussed in a academic context it is preferred to refer to them using their scientific names rather than using your local language, once again to aid understanding.
I suppose the point I am building towards is that it doesn't matter whether a standard is adopted internally within a country as to whether or not the standard has meaning, what matters is that the standard is adopted for purposes of cross national communication.
For an example more relevant to this sort of context of weekends and such, if you are running a multinational team and had to handle scheduling, it would be best practice to adopt worksheets that start the week on a Monday as while that may not be the standard used in your own country it is the standard that has been established internationally.
