To list the 4 countries - CHINA, CHAD,CANADA & CHILE you need only 8 distinct letters: A,C,D,E,H,I,L & N.

Find a 10-member subset of ABC such that enables to create the longest list of currently existing countries.

The following restrictions apply:
- Only UN current official members
- English spelling of names e.g. Spain, not Espana
- No abbreviations!

Google's list https://www.un.org/en/member-states/ recommended as database.