Many years ago, a maths teacher at my school used to say that it was far easier to become a billionaire in the United States than in Britain. He was not referring to the entrepreneurial skills and attitudes of the Americans and the phlegmatism of the British, but rather to the fact that 1 dollar was worth less than 1 pound, and that the American billion was – or perhaps a little more accurately had been in the past – smaller than the British billion. Historically a billion meant a million million (1,000,000,000,000) in British English. However, in modern British English, a billion is a thousand million (1,000,000,000) just like in American English: Oxford Dictionaries describes the definition of a million million as dated, British. I certainly have not come across an instance recently in official reports or in the media in the UK where a billion signified a million million.
It helps that a billion means the same thing in the English-speaking countries (a thousand million), otherwise it would cause a lot of confusion, but this has created faux amis: billion and Billion in French and German respectively are a million million, i.e. a trillion in English and a billion in the old British usage, and for a billion in English i.e. a thousand million, the equivalent words are milliard and Milliarde. And the differences continue: trillion and Trillion in French and German are quintillion in English, and so on.
Naturally translators are well aware of these issues, so it is rare to find mistakes in written text, but in conversation, it can be easy to forget that a billion in English is not the same as a billion in French or German.