I thought of that before and I took German in college, but other countries with other languages don't usually use Engish words like "European". The Germans don't call their own country "Germany" even. It's Deutschland. United States in German is "Vereinigte Staaten". The word for European is "europäisch" so perhaps they at least have the first part in common, but that isn't necessarily going to hold true for all European countries. So why use a non-English convention for an English word? In any case, this has gone on way too long. They can call it anything they like. My point is that it simply sounds "odd" to most of us which is why so many assume it's got an 's' in the plural.
So long I've just been lurking, 'cause I want to buy a Macbook.... But now I feel this irresistible urge to clarify...
Euro of course is not an English word, so a Non-English convention is not out of place at all.
"Eurṓpē" is a very old greek word that means something like "women with a wide face" - but most prominently, it was the name of a queen daughter, that, as the old Greek and Roman mythologies say, was kidnapped and impregnated by Godfather Zeus.
The expression "Euro" is nothing but the extracted root of that old greek word (as you might know, the old Greece stands at the beginning of European culture, and much of what is attributed to the Romans is in fact a Greek invention).
Everybody in Europe says "Euro" (except in Bulgaria, because their language does not have the root "Euro". Bulgarians say "Ewropa" instead of Europe....).
Euro as well as
cent do not add an s in their plural form (or anything else, for that matter). "Cents" is only sometimes and in some countries used when referring to the actual coins. May I remind you that there are several currencies in the world that work just the same way: Russian rubel, Turkisch lire, Japanese yen, etc. etc.
That's all for today, now I will draw my attention back to the question: black book or white book (oh, and Zeus, I might add, kidnapped Europa in the disguise of a white bull...

)