So, many country nationalities are written by adding +jin to the country name like Itaria-jin イタリア人 , Oranda-jin オランダ人, Kanada-jin カナダ人, Supein-jin スペイン人 , etc.
but there are some like american who can be written 米国人 Beikokujin or アメリカ人 Amerikajin.
And some others you only commonly find it with an original name like ドイツ人 Doitsujin or 中国人 Chūgokujin. How about countries like these last ones. Can they also be written country name + jin or it's only valid to call them with their original names?