My week starts Monday!

So I am really not using the in-game calendar a lot, as only Birthday parties is listed in my calendar, and fortunately these are far in between (I don't like birthday parties). 
But now I have a bunch of birthday parties coming up, and the calendar confuses and annoys me, because first day of the week is apparently Sunday. I thought it was an issue in my settings, most calendars provide the option of selecting first week day, but no. 

If I am not mistaken this game (TS4) has existed for a decade, and the calendar still, in this regard, only favors a small number of countries. 
According to the statistics I have obtained, around 40-50 countries worldwide start the week on Sunday, while almost 150 countries start the week on Mondays. Entire continents are using the concept of First weekday is Monday, Europe use ISO-8601 (Monday start), Russia use First weekday is Monday, and South America, Asia and Africa is using the ISO convention (Monday start) in software and government calendars, and it is broadly used among the populations. International Organizations use Monday as first day of the week. 
But The Sims are stuck in a vacuum that disregard the convention of the majority of the worlds population. 

I assume that I am not the only one who is annoyed and confused by this, and I am close to considering as a Bug, that needs to be fixed.
Thank you.

Smile it's Sunday.