Consistent naming of subnational flags #85
Description
Some subnational flags have two hyphenated two letter codes, like cn-xj (China, Xinjiang) and in-ka (India, Karnataka), while others which are prima facie very similar, have standalone codes, either abbreviated like hk (Hong Kong) or spelled out in full like mizoram (Mizoram), instead of cn-hk (China, Hong Kong) and in-mz (India, Mizoram).
EDIT: I have since learned that the relevant standard is ISO 3166-2.