Php dies with Uncaught Error: Call to undefined function Bright\\mb_encode_numericentity()

A lot of newer Linux servers do not have PHP Multibyte modules installed by default. A simple solution is often to install php-mbstring.

# Debian/Ubuntu
sudo apt install php-mbstring    # apt-get back in the day

# Fedora/RHEL

sudo yum install php-mbstring

Don't forget to restart nginx or apache!!!