Can't change language back to English in Kubuntu 19.04

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

1. sudo locale-gen en_US.UTF-8 or
2. sudo localectl set-locale LANG=en_US.utf8 or
3. 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 :)

I have the Kubuntu backports ppa enabled on my system and so I may have a more recent version of Plasma than provided by vanilla Kubuntu 19.04.

Operating System: Kubuntu 19.04
KDE Plasma Version: 5.16.4
KDE Frameworks Version: 5.60.0
Qt Version: 5.12.2
Kernel Version: 5.0.0-23-generic
OS Type: 64-bit

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When I opened System Settings > Regional Settings > Language for the first time, no languages were listed under Configure Plasma Translations. So I first added American English and then added Hindi. I tried to add Marathi as the third language and that caused a System Settings crash. So I stayed with just the two languages.

To switch languages, click on the row listing the language you want and then bring it to the top as shown:

The change of language needs a log out:

As you can see, the translations are partial. The translation team would appreciate help in this respect if you have the time to spare.