What about people in those countries who cant read?
McDonald's plan to get people to understand them is to put the words next to the icons to get people to understand the icons, which also wouldn't help if you can't read.
Sure, only a relatively small percentage of the population of Germany/Poland/etc may not be able to read. But how many of those visit McDonald's? Do they visit it more or less often than other categories of people? How important is it for them to be able to understand these icons? Is the cost of developing icons/signs they also understand more or less than the amount of trouble them not understanding these icons would bring? Are we talking about actual literacy or the more nebulous category of "functional literacy"?
There are cases where "devil's advocate"-style questions are worthwhile, and I'd argue that they're worth at least considering in this case.