Time alone will tell - but, it is entirely possible that Europe in 200-300 years will have a majority Muslim population, and if the lack of integration (that is prevalent there now, unlike in the USA) persists, then the 'one tongue' won't be English, either!
I assume that the Muslim-influx in Europe is NOT predominantly from French speaking areas of the world - though there are certainly many of them, but more likely bearing Arabic, Farsi, or some blend of Urdu - Pashto - Punjabi tongues.
I think what we've been seeing in the past few years is that as the world grows smaller through internet (etc) communication, the more people want to be different and have their own identity. While there will be a need for a lingua franca (which may or may not be English) for global communication, people will be guarding their own language/culture more perhaps. Maybe that is daydreaming but the very fact that Americymru exists and there are cultural "clubs", for want of a better word, all around the world must mean something.
Oh - I don't disagree. People will always want to be 'guarding their own language/culture' - perhaps even more so as globalization vamps up. One point I was making - that naturally is less evident to those who have only lived on one side of the Atlantic - is that in the US, 'foreign nationals' tend to integrate far more than they do in the UK and continental Europe, where they tend to gravitate to, and stay in, 'enclaves of their own type'. At least, it was that way in my day - maybe it is different now. Back then, Bradford (Yorkshire) was known as Karachi-West.
Oh, I'm sure you're right about the US; although I've visited a number of times, I've never been there long enough to know. Funny you should have mentioned Bradford as there was a short series of programmes called "Make Bradford British" in the past few weeks.