Unless you're switching from e.g. Java to e.g. Prolog or Erlang (or Haskell...), is it really useful for learning a new language? I mean, when learning a new language, the basic syntax is the easiest part anyway, but the ecosystem/batteries/best_practices is where the main bottleneck is. And I have an impression that Project Euler problems will help you only with the very basics of the language.
