Iso-codes is a directy dependency of plasma-workspace, that's why for
most uses, it was not an issue. I saw missing iso-codes triggered a lot
autotests to fail for itinerary, so I got in contact with upstream
author Volker Krause and they said - yepp you are missing iso-codes.

From README.md:

Some of this information is read from iso-codes at runtime
(/usr/share/iso-codes/json), so the iso-codes data files and translation
catalogs need to be installed.