That's not universally true. In my country, German was the widely accepted and taught second language until WW2. Since then it's been English.
Which in our case is false. We stopped learning German as a second language because of the Nazi aggression and atrocities during WW2, and started learning English as a second language due to their aid and closer relations during the war.
But yes, it's obviously not because of any linguistic merit.
ETA: They lost WW1 too, but German remained our #1 foreign language.
No significant minority of ethnic Germans, and I think trade with Germany and the UK was roughly comparable.