It's not a question of being American, but rather of being a native English language speaker. The second language of choice of most people is English, as it's become the lingua franca
of international trade, aviation, the internet, entertainment and so on, not because they live near English-speaking countries.
Language prevelance is largely based on age, education, and type of employment. My experience living in various European and Asian countries is that:
-Younger people tend to speak English
-More educated people tend to speak English
-Professionals tend to speak English
You therefore end up with the decidedly odd experience of talking to Dutch people who speak English with an American accent by virtue of watching American TV and listening to American music.
Another factor are colonial relationships - bits of the world that the Brits owned tend to speak English, and so on.
Patterns of migration and cultural links are also important. You therefore end up with a lot of German speakers in South America and Australia. It would therefore be reasonable, given how many Americans describe themselves as [Other country]-Americans to also speak or at least have some grasp of that other language. I certainly see the same in Australians - huge numbers of Greeks, Lebanese, and Vietnamese-origined people speaking both in the area I lived in.
In the UK, migrant populations tend to speak English and their 'mother' tongue - Urdu, Hindi, Mandarin, and so on. British-origin Brits tend just speak English, plus a tiny smattering of 'schoolboy' French or German and so on.
It is, I think, purely lazieness that means we don't learn other languages. We don't have to. Our language is the most common one. I tried so desperately hard to learn Dutch and BCS when living in those respective countries, but my experience was the same - friendly locals who say things like "You are trying ot learn my language? How charming. But please, let me practice my English on you". Needless to say, my conversational Dutch is very limited indeed.
Or Africans speak German?
Quite a lot will speak Dutch