The keys are for a specific context, so that makes collisions unlikely. You'll notice the example context "turned-over-ezic-docs" has only three strings in it. Of course, if he ever did have a key collision, it would be easy to solve. At worst, he'd have to replace the English strings with random, unique strings and make English a translation just like any other. He decided he'd pay that toll only if he needed to. And he didn't need to.