Q:

How to change the first day of week on wingpanel calendar?

I'd like to change the first day of week on the little calendar that shows up at the wingpanel. At the current state it shows Sunday as the first day of the week, but I'd like it to be Monday. How can I change this?
Thank you!

A:

Use a locale from a culture where that is the norm.
You can try to make that a sticky setting for your user in the system, by putting something like that in ~/.xsessionrc
export LANG=en_US.UTF-8
export LANGUAGE=en_US.utf-8
export LC_TIME=en_GB.UTF-8
export LC_MEASUREMENT=en_GB.UTF-8

Which is basically "I want system messages in American, but time and measurement in UK English". Monday is the first day of the week in UK culture.
Log out and back in for that to work.
Or, you could try make that a system-wide change.
Assuming your locale outputs LANG=en_US.UTF-8, find and change first_weekday 1 to first_weekday 2 in the US locale file (do a sudo nano /usr/share/i18n/locales/en_US). Then do a sudo locale-gen and reboot. 
The latter is not recommended in a server setting, but you should be fine on your own machine.

