[wpietri]

For that example, I'd say the text wouldn't help most people regardless of language. One would have to know a fair bit about the mechanics of currency conversion. I happen to know that, and I still would have to pick randomly, because this would come down to exchange rates that the interface isn't exposing.

The correct user-focused interface solution for that particular problem is to show the actual costs next to each button. And then I'd think one would make the cheaper option the obvious default (e.g., bigger, greener), with the more expensive option less favored.