Hello old-welsh-surfer,
Welcome to Apple Support Communities. I understand that the Maps app on your iMac shows the African country names in Arabic. Other countries such as Russia show in Russian. You’re using macOS Catalaina on your iMac. Your iOS device using iOS 13 shows the countries in Maps app in English. I’m happy to help.
Maps on Mac has the option of showing map labels in either the local language for that area, or in your preferred language. To show all map labels in English, make sure the following setting is selected:
"Set your preferred language for map labels: To always use your computer’s preferred language for map labels, regardless of the language of the region you’re viewing, choose View > Labels > Always Show Labels in [language]. To learn more, see Change the language your Mac uses."
Customize your map view in Maps on Mac - Apple Support
Take care.