Hello,
I need to set the first day of the week to monday. Currently, it is set to sunday on my discourse trial.
I’ve search all web site settings and personal preferences but could not figure out how to setup monday as the first day of the week on my category calendars
I’m not sure that this is the correct answer but you could try setting the working days as per the image below and see what happens.
Hello,
Thanks for your reply.
My working days are already set as you suggest.
But it doesn’t help in my case.
Sorry
This doesn’t help you a bit, but I stopped to use it just because sunday was the first day of week. And the most of world uses monday, so for me it was like forced to use inches, furlongs and stones 
But I reckoned they fixed it at some point. But apparently not.
I’m afraid I don’t think this is currently possible at the moment. The Upcoming Events calendar begins on Sunday, whereas the topic calendars start on Monday.
Depending on your use case, you could use the topic calendar instead and add it to a category view?
We create the events in several topics that have to be discussed and are part of sub categories.
So I think I need category calendars.
I think the Events feature of the plugin does sound exactly what you need for that so the topic calendars may not be a good workaround.
I agree that it would be nice to be able to choose your start day of the week for the Upcoming Events calendar. I’ll slide this over to a feature request and see if others feel the same. 
It was also asked here as well, so you’re not alone:
Sorry (not really 
) nagging, but at least ability to use globally the most used starting day monday should not be any feature request. It is major lack of UX.
I agree. My users are getting completely lost with weeks starting on sunday.
Please vote for this if it matters to you 
Sure, voting is good. But… this Monday/Sunday issue has been in the spotlight and asked about so many times that CDCK is aware of the need for it, even without any voting.
The reason we are still stuck with a calendar system used by a minority globally is different from a lack of votes.
I understand, it was not obvious.
May I be curious what that is?
I don’t know. My bet goes to some technically difficulties where the starting point was purely US-based, and changing that would lead to some difficulties. Otherwise it would be fixed already.
But I’m just guessing.
It looked like you knew exactly That information would be interesting for possible contributors.
All I know exacly is this
I see the plugin uses Full Calendar to display de calendar
Full Calendar allows to set the weekNumberCalculation to ISO when you render de calendar so weeks start on Monday. There is also a firstDay setting.
I don’t have much time now to investigate but it would be relatively simple for the plugin author to include a new setting to allow us to define the first day and then pass that to the calendar render, same as the timezone is now being passed.
Did you know it’s hard coded to Monday almost everywhere else (surprised me as well)
Ideally this would be dependent on user preferences (not on an admin setting).
I’ve taken a look at the code, since this issue has been annoying me for a long time too. There are three places in the code where FullCalendar is initialized. In one of them firstDay: 1 is already present. Discourse core hardcodes it to 1 as well.
I’ve made a PR that adds firstDay: 1 in the two missing places.
This is far from ideal but at least it brings consistency.
The fix is now committed to the main branch, so I guess we should expect to see this in the next release 
Thanks @RGJ !