@heri because they write in English (it is "miliarda" in Czech, too)
Adopting "Milliarde" into Euro-english vocabluary is an interesting option. It would be perfectly clear for most EU citizens. Also, India (to stay ontopic) has adopted their "crore" and "lakh" into everyday English. But while cryptical, there is zero chance of confusion with other one-word units...
Using both "Millarde" and "Billon" would be confusing, but "Billiard" not so much (unless confused with the table game of billard :-)). It would be fine, if we all agreed to talk about "1000 Milliards" instead of Trilion/Billion.
There precedens for unifying numbering systems is French soixante-dix, quatre-vingts, quatre-vingts-dix and vs. Swiss septante, huitante, nonante. They may sound strange to each other, but the meaning is unique and understandable.
Milliarde may sound weird to British and Americans, but just like with crore and lakh, there is zero chance of incorrect interpretion (unlike Billion). So yes: adding Milliarde into Euro-english is good idea. We can make Fedi poll about it :-)
@EUCommission