It would seem like “Nigerian” is already taken.
Nigerien as opposed to Nigerian. Nowadays the pronunciation would be different: Nee-zhair-ee-en rather than nye-jeer-ee-ann
Confusingly, Nigerien. Note the difference in spelling. As spoken it is an easier distinction, because as a former French colony it usually given a French pronunciation.
Well, that answers that. Except that I have never accepted the pronunciation of the country’s name as “nee-ZHAIR”, always preferring “NYE-jer.” After all, in English we refer to France as "FRANTS’, not “FRAWnSS”.
One of my friends here in Beijing is actually from Niger. He spells the demonym as indicated above: Nigerien and pronounces it /niːˈʒɛərɪən/. Oh, he also pronounces the name of his country with the French pronunciation.
Not really an apt comparison as there is no “Francia” or something equally similar.
There was a Francia, but Louis the Pious couldn’t figure out which kid to give it to so that ended.
I grew up in an area where a person from Canada was a Canadien. And you didn’t argue because he had a hockey stick.