I have two call directory extensions, each with InfoPlist.strings in en.lproj and nb.lproj directories. In these files I've defined CFBundleDisplayName for both locales.
These names are displayed under Settings -> Phone -> Call Blocking & Identification. On iOS 12.2 the names are displayed correctly in both Norwegian and English.
Testing on iOS 15.3 the English names are displayed even when device language is set to Norwegian.
Worth noting: When updating the English versions of CFBundleDisplayName this is immediately reflected in Call Blocking & Identification page with Norwegian device language.
As this feature requires a real device, I'm unable to test on iOS 13 and 14.