I´m european and the natural way for me is period for thousands and commas for decimals, although I´m aware of the imperial way, with commas for thousands and periods for decimals.
Another important difference is that in Europe we understand a billion as a million of millions (10^12), not a thousand of millions (10^9). For us, a 10^9 is a miliard. Luckily I´m also aware of the use of billions for 10^12 and whenever I read it on a US or UK text I understand correctly. Otherwise, saying that there are 7 billion people on Earth would be an extreme exageration...
Another important difference is that in Europe we understand a billion as a million of millions (10^12), not a thousand of millions (10^9). For us, a 10^9 is a miliard. Luckily I´m also aware of the use of billions for 10^12 and whenever I read it on a US or UK text I understand correctly. Otherwise, saying that there are 7 billion people on Earth would be an extreme exageration...