``date`` in terminal now in 12hr format on Debian Buster

Question

Since updating to Debian Buster, running date on the terminal shows the clock in AM/PM format instead of 24hr clock. This is new and is happening on all updated installations.

Docker container:

yeri@b9b3e889fd76 ~ $ date
Thu 01 Aug 2019 11:28:25 PM +08

Native host:

liana ~ # date
Thu 01 Aug 2019 11:32:44 PM +08

Digital Ocean:

ui0 ~ # date
Thu 01 Aug 2019 05:33:11 PM CEST

This is quite annoying and I didn't ask for this -- however can't find the settings to change it.

The only thing I can think of is that the locale is set to US; but that was the case before as well (Debian 9):

ui0 ~ # cat /etc/default/locale 
#  File generated by update-locale
LANG=en_US.UTF-8

yeri@b9b3e889fd76 ~ $ locale
LANG=en_US.UTF-8
LANGUAGE=
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=en_US.UTF-8

yeri@b9b3e889fd76 ~ $ date
Sun 04 Aug 2019 04:39:14 PM +08

yeri@b9b3e889fd76 ~ $ locale date_fmt
%a %d %b %Y %r %Z

yeri@b9b3e889fd76 ~ $ locale -k LC_TIME
abday="Sun;Mon;Tue;Wed;Thu;Fri;Sat"
day="Sunday;Monday;Tuesday;Wednesday;Thursday;Friday;Saturday"
abmon="Jan;Feb;Mar;Apr;May;Jun;Jul;Aug;Sep;Oct;Nov;Dec"
mon="January;February;March;April;May;June;July;August;September;October;November;December"
am_pm="AM;PM"
d_t_fmt="%a %d %b %Y %r %Z"
d_fmt="%m/%d/%Y"
t_fmt="%r"
t_fmt_ampm="%I:%M:%S %p"
era=
era_year=""
era_d_fmt=""
alt_digits=
era_d_t_fmt=""
era_t_fmt=""
time-era-num-entries=0
time-era-entries="S"
week-ndays=7
week-1stday=19971130
week-1stweek=1
first_weekday=1
first_workday=2
cal_direction=1
timezone=""
date_fmt="%a %d %b %Y %r %Z"
time-codeset="UTF-8"
alt_mon="January;February;March;April;May;June;July;August;September;October;November;December"
ab_alt_mon="Jan;Feb;Mar;Apr;May;Jun;Jul;Aug;Sep;Oct;Nov;Dec"

Answer 1

It seems the reason for this change is that in buster the en_US locale is updated. Since it is meant to represent US customs, which is to specify time in the 12 hour format, time is now shown as such, even though it may come as a surprise to everyone who has relied on the old behavior.

A solution, as already mentioned by @JosefZ in the comments, is to use a locale that has the time settings that you want, for example C.UTF-8. To make this change permanent on Debian you'd run:

update-locale LC_TIME=C.UTF-8

This sets the definition for LC_TIME in the file /etc/default/locale.

You can find more information about the change itself in Debian bug #877900