It accepts about 180 country names in any case, with or without accents, plus short forms such as USA and UK. A partial name works if only one country matches.
Start typing and choose from the list, or type the full name. Aliases include USA, UK, UAE, Czech Republic and Côte d’Ivoire. A partial name such as Switz is accepted when it matches one country; if it matches several, such as Korea or Congo, the game asks which you meant.
A name that is not recognised does not use up a guess.
See also How many guesses you get. For tips, read the Closer or Farther tips and strategy.