The Unicode symbols for flags consist of a special set of combining country-code letters that when used in two-character combinations compose into flags. That solution ensures that the Unicode standard doesn't hard-code the existing list of countries and country codes. In addition to future-proofing, that also avoids dealing with disputed regions that not everyone recognizes as countries.

See https://en.wikipedia.org/wiki/Regional_Indicator_Symbol .

I parse those as ISO 3166-1 alpha-2 country codes:

AU AT BE CL CZ EE FI FR DE HK HU IE IL LT NL NO PL SE CH GB

Australia, Austria, Belgium, Chile, Czech Republic, Estonia, Finland, France, Germany, Hong Kong, Hungary, Ireland, Israel, Lithuania, Netherlands, Norway, Poland, Sweden, Switzerland, United Kingdom

Turns out they're in alpha order by country name, too.

When I imagine, in my head, "hmm, how can I present a string of 20 x 2 chars, what is the best way I can confuse the reader?" this is the exact solution I come up with, also.