Lingua franca literally means “French Language”. It means the common tongue of the world, which right now is English.
Rabbi horowitz has written about people whose first language is Yiddish and can’t get a real job because they can’t function in society. So I do not give credit to those who do so, as they are dooming their son to limited career choices (not everyone is meant to become a gadol hador) although I understand their hava amina (“I would have said”, ie a logical thought that is later refuted).