Flat country flags were downloaded through FlagCDN (https://flagcdn.com/),
which distributes flag-icons (https://github.com/lipis/flag-icons) under the
MIT License. Regional flags are from flag-icons v7.3.2 under the same license.

The Esperanto flag is sourced from Wikimedia Commons, “Flag of Esperanto.svg”
(https://commons.wikimedia.org/wiki/File:Flag_of_Esperanto.svg), public domain.
