The following worked for me (I did this after reading your request and it works!)
Of course, back up your files before making any edits.
Open: portal/includes/mini_cal/mini_cal_config.php
Find:
// First Day of the Week - 0=Sunday, 1=Monday...6=Saturday
// if you change this remember to change the short day names in lang_main_mini_cal.php
define('MINI_CAL_FDOW', 1);
In-Line Find: define('MINI_CAL_FDOW', 1);
Replace with: define('MINI_CAL_FDOW', 0)
;
Open: language/en/mods/lang_portal.php
Find:
//if you change the first day of the week in constants.php, you should change values for the short day names accordingly
// e.g. FDOW = Sunday -> $lang['mini_cal']['day'][1] = 'Su'; ... $lang['mini_cal']['day'][7] = 'Sa';
// FDOW = Monday -> $lang['mini_cal']['day'][1] = 'Mo'; ... $lang['mini_cal']['day'][7] = 'Su';
'mini_cal' => array(
'day' => array(
'1' => 'Mo',
'2' => 'Tu',
'3' => 'We',
'4' => 'Th',
'5' => 'Fr',
'6' => 'Sa',
'7' => 'Su',
In-Line find:
'1' => 'Mo',
'2' => 'Tu',
'3' => 'We',
'4' => 'Th',
'5' => 'Fr',
'6' => 'Sa',
'7' => 'Su',
Replace with:
'2' => 'Mo',
'3' => 'Tu',
'4' => 'We',
'5' => 'Th',
'6' => 'Fr',
'7' => 'Sa',
'1' => 'Su',
Save all changes. Purge your cache.
Final Result:
