Those kind of rewrites originated in the 1940s, when Europeans were a bit queasy about Americanization and didn't really want their kids exposed to too much American "propaganda". Disney in general had this "way too American" stigma at the time, so localizing the translations like that made it at least come across that this may be "mass-produced American garbage", but it's at least being edited by locals that care about your kids.
In the 1940s, that's understandable. But I grew up in the early nineties, and it was still like that.
Because of tradition! What would older Duck fans say if these translation details were revised after so many decades? Speaking as someone who grew up with the comics in Norwegian, it would be very strange to see Scrooge talk about the first coin he earned as an American "dime" in our local editions rather than a Norwegian "tiøring". Despite the fact that I of course knew it wasn't a "tiøring" originally.
In Brazillian translations, the currency is not US Dollars, not even the Brazillian Real. It's "Patacas", a fictitius money. So, I think it makes sense for brazillian readers that those patacas coins could be golden, or even of any color, because it doesn't exist in real life.
Oh, absolutely, it makes sense when the text specifies a fictitious currency. Isn't that the case in Germany, too? The "taler"? You can have all the gold coins you want in that case. And then there are all the countries where Duckburg is depicted at least some of the time as located in the country where the comics are published, and the symbol on the bin is the symbol of the local currency. Some of those countries might have more gold-colored coinage than the USA does. I'm just talking about the coloring I want to see in English-language printings.
The nice thing about "Taler" is that it used to be a currency in parts of the German speaking area, a long time ago. So it's not a fantasy word, but it's also nothing that's still in use. Bonus: It's etymologically related to "Dollar" (in fact, pretty much the same word).