ubuntu locale and timezone

assume for example:

date/time in it_IT with Europe/Rome timezone
messages, numbers and all the others in en_US
install required packages

apt install locales

generate locales for en, it

locale-gen en_US.UTF-8 it_IT.UTF-8

view current settings

locale

set default lang en while set time to it

update-locale LC_TIME=it_IT.UTF-8

this will change /etc/default/locale as follows

LANG=C.UTF-8
LC_TIME=it_IT.UTF-8

set the Europe/Rome timezone

timedatectl set-timezone Europe/Rome

this will change /etc/timezone as follows

Europe/Rome

all at once

apt install locales
locale-gen en_US.UTF-8 it_IT.UTF-8
update-locale LC_TIME=it_IT.UTF-8
timedatectl set-timezone Europe/Rome

for desktop environment you might need to comment out settings in ~/.pam_environment