The following allows you to very easily flip between languages and country on Android.

AndroidEasySetLangCountry

The following allows you to very easily flip between languages and country on Android.

This will IMMEDIATELY cause the change without even needing to shut down the target testing app.
(That is, the currently displayed page will reloaded.)

You first need to install this APP on the phone:
https://play.google.com/store/apps/details?id=net.sanapeli.adbchangelanguage&hl=en

Then to flip copy and paste one of the lines below in a terminal. 

For other language and country codes see:
  https://en.wikipedia.org/wiki/ISO_3166-1
  https://www.loc.gov/standards/iso639-2/php/code_list.php

# United States
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country US
# Austria - Germany
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language de -e country AT
# Belgium 
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language nl -e country BE
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language fr -e country BE
# Denmark
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language da -e country DK
# Finland
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language fi -e country FI
# France
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language fr -e country FR
# Germany
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language de -e country DE
# Italy
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language it -e country IT
# Luxembourg
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language fr -e country LU
# Egypt
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country EG
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country EG
# Netherlands
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language nl -e country NL
# Norway
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language no -e country NO
# Poland
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language pl -e country PL
# Portugal
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language pt -e country PT
# Sweden
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language sv -e country SE
# Switzerland
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language de -e country CH
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language fr -e country CH
# Spain
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language es -e country ES
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country ES
# South Africa
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en-ZA -e country ZA
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language af -e country ZA
# Great Britain
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en-GB -e country GB
# Russia
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ru -e country RU
# Slovakia
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language sk -e country SK
# Turkey
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language tr -e country TR
# Oman
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country OM
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country OM
# Saudi Arabia
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country SA
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country SA
# United Arab Emirates
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country AE
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country AE
# Bahrain
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country BH
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country BH
# Kuwait
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country KW
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country KW
# Lebanon
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country LB
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country LB
# Jordan
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country JO
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country JO
# Qatar
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language ar -e country QA
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language en -e country QA

# NOT IN LIST
# French - Canada
adb shell am start -n net.sanapeli.adbchangelanguage/.AdbChangeLanguage -e language fr -e country CA