export LC_TIME="en_GB.UTF-8"		# date format (still English, but weeks start on monday)

it works for orage...

about cal, on xubuntu oneiric it has a weird bug, it ignores custom locales: if this is your problem, substitute cal with

ncal -C -h

I want to change the starting day of the week from Sunday to Monday in Orage and cal.

My locale output is:

LANG=en_US.UTF-8
LANGUAGE=en_US:en
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

I tried changing "first_weekday" value in /usr/share/i18n/locales/en_US and "locale-gen" after that, but nothing changed after restarting X.
I tried exporting LC_TIME as en_GB, also nothing changed.

How do I do this?