For example
"Don Quijote" Jarvan for Spain

or create a new one for a country who already have it; like karate Lee Sin without
worry about Samurai Master Yi Samurai

Black Face Lulu for Africa.

Reichskommissar Swain, in gray uniform and including "black eagle" alternate form.

Carnaval Mordekaiser, colorfully garbed and full of festive Brazilian spirit.

Jihad Kog'Maw, with an exciting new passive animation.

French Mime Shaco, exaggerated movements and null sound set.

What about U.S marine Graves?

Well Muse Sona is pretty much Greek.

Slapshot Tryndamere for that Canadian hockey spirit.

Replace his sword with a hockey stick, switch his horned helment for a red hockey one, give him a white jersey with a red maple leaf on it, change his movement animations to be smoother, a more fluid skating motion, essentially, and maybe take the Arcade Sona route of actually changing the kill/death interface. It could shout out "Goaaaaaaaaaal!" (or "Enemy Goaaaaaaaaaal!") upon kills and deaths, and could signal the end of a game with a buzzer noise like you would get at any professional hockey game.

Dialogue replaced with horrible hockey puns and poorly-done Canadian-isms is optional, but Riot would probably go for it.