apt-get update &&
apt-get install -y language-pack-en-base &&
export LC_ALL=en_US.UTF-8 &&
export LANG=en_US.UTF-8 &&
apt-get install -y software-properties-common &&
add-apt-repository -y ppa:ondrej/php5-5.6 &&
add-apt-repository -y ppa:ondrej/mariadb-10.0 && 
apt-get update && 
apt-get -y upgrade

• https://github.com/oerdnj/deb.sury.org/issues/56
• http://geekdecoder.com/ubuntu-16-04-xenial-downgrade-php-7-php-5-6/