How small does the British Empire have to be for English not to be the unrivaled global Lingua Franca, even with America being like in OTL?
Maybe if the US has more Spanish speakers, and maybe preserve the German speaking populations in the mid-west, and the Americans will grow much more open to learning new languages. With that there might be enough Francophiles in the US to keep French on top, or if the Germans win a pseudo-WWI type thing you might see German rising to be the language of choice as the Americans sort of know it already too.