Apologies, I finally had some time to figure out why the installer is breaking. During the install, deamon.py on line 27 opens the country codes file (csr_country_codes.tsv) and when it reaches byte 0xc3 (position 795) of that file, namely the first letter of the wonderful Åland Islands, it just breaks. The real kicker is… UpCloud must be borking the 18.04 install as the VPS gets provisioned without a specified locale. So, running this ONCE the server is provisioned but BEFORE you install MiaB fixes it:
locale-gen en_US.UTF-8
update-locale LANG=en_US.UTF-8
reboot
This, clearly, set the locale, and, most importantly, sets the system-wide encoding to be used. After that, there are no issues with the install and everything proceeds as planned.
Guess I have to ping UpCloud to fix their deployments, or maybe it can be added as a script.