[lorenzhs]

Several countries have articles in German, most don't. Plural countries (USA, UAE) have the plural article, which in the standard form is the same as the feminine article ("die") which makes for even more confusion, but when used in a case changes differently ("in den USA" vs "in der Schweiz") :)

Some feminine countries: Switzerland, the Dominican Republic, Mongolia, Slovakia, Turkey, Ukraine, Central African Republic.

Male, in addition to your own list: Niger (!= Nigeria), Sudan, Vatican.

Neutral: UK (because kingdom is a neutral noun in German), potentially others