Root cause:
When we add language via System Settings > Regional Settings, it is added as KDE Plasma's (Desktop Environment's) Language and not System Language. Hence, though System Language shows English (run locale in terminal), we still see our desktop in the language specified in Regional Settings.
This is also the reason why using
sudo locale-gen en_US.UTF-8 or sudo localectl set-locale LANG=en_US.utf8 or - Putting
export LANG=en_US.utf8 in ~/.bashrc and running source ~/.bashrc
doesn't effect the language setting set in Regional Setting.
Solution:
Go to ~/.config/plasma-locale-settings.sh, open it and ensure it contains following:
# Generated script, do not edit
# Exports language-format specific env vars from startkde.
# This script has been generated from kcmshell5 formats.
# It will automatically be overwritten from there.
# I am from India, hence en_IN, shouldn't matter much
export LANG=en_IN
export LANGUAGE=en_US
then, go to ~/.config/plasma-localerc, open it and ensure it contains following:
[Formats]
LANG=en_IN
[Translations]
LANGUAGE=en_US
Shutdown the computer and start again. You should be back on English. If not, do let me know by comment :)
Best Answer
Open a terminal and type the command:
This will open the system preferences application in English, and under "Language Support" you can change the language to what you want.