Various quick fixes encountered

Unlike most sites, committing long-ass mumbling about meaningless nonsense before single-line quick fix, this section is to the point but needs your attention. Every word matters, dont skip lines.

E: sudo: add-apt-repository: command not found
S: sudo apt-get install software-properties-common 

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E: Unable to locate package python3.6
E: Couldn't find any package by glob 'python3.6'
E: Couldn't find any package by regex 'python3.6'

S:
sudo add-apt-repository ppa:jonathonf/python-3.6
sudo apt-get update
sudo apt-get install python3.6

(ref and more:) http://ubuntuhandbook.org/index.php/2017/07/install-python-3-6-1-in-ubuntu-16-04-lts/

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E: perl: warning: Setting locale failed.
E: perl: warning: Please check that your locale settings:


S: (reset locales, needs reboot)

sudo update-locale LANG=en_US.UTF-8
sudo update-locale LANGUAGE=en_US.UTF-8
sudo update-locale LC_CTYPE=en_US.UTF-8
sudo update-locale LC_NUMERIC=en_US.UTF-8
sudo update-locale LC_TIME=en_US.UTF-8
sudo update-locale LC_COLLATE=en_US.UTF-8
sudo update-locale LC_MONETARY=en_US.UTF-8
sudo update-locale LC_MESSAGES=en_US.UTF-8
sudo update-locale LC_PAPER=en_US.UTF-8
sudo update-locale LC_NAME=en_US.UTF-8
sudo update-locale LC_ADDRESS=en_US.UTF-8
sudo update-locale LC_TELEPHONE=en_US.UTF-8
sudo update-locale LC_MEASUREMENT=en_US.UTF-8
sudo update-locale LC_IDENTIFICATION=en_US.UTF-8
sudo update-locale LC_ALL=en_US.UTF-8
sudo dpkg-reconfigure locales