Fix languageCode mismatched issue

[ming-chu]

Fix language code mismatch issue due to the key of languageCode being converted to lowercase before use.

in the file lib/countries.dart all keys containing capital letters were affected under nameTranslations:

      "pt_BR": "Afeganistão",
      "sr-Cyrl": "Авганистан",
      "sr-Latn": "Avganistan",
      "zh_TW": "阿富汗",