Germany may be a poor example. I do happen to live in your example (Germany). And it's far fetched to say Germany isn't diverse. You know how many guest workers to refugees we have taken in since the 60s? I just googled "foreigner percentage US" and the same for Germany. It's 13% for US and 18% for Germany. This is non-inclusive of the millions of second or third generation Turkish here.

Also, if you have ever been a foreigner in Germany like myself, you would know that these number are far overstated for German people that can usefully speak another language. There are better examples for your point, like Holland or Luxemburg with genuinely high second or third language levels. Or you can also look at native English countries and see the US isn't alone in it's low adoption of second languages.