The rules differ between English and French (of course they do lol!):
- in English: nationalities all take capital letters, either used as adjectives (This is an English rug) or as nouns (There are two Frenchmen here).
- in French: you won't use a capital letter when using nationalities as adjectives (C'est un tapis anglais), but you will when used as nouns (Il y a deux Français ici).
I hope that's helpful!
Bonne journée !