Many complaints are that non-ASCII characters (which all but one European languages have natively) are not allowed. While I agree that allowing them would be good for password security past experience has made me paranoid. Not all systems handle non-ASCII the same way, so when you change browsers or they upgrade their system your password might no longer work. Today Unicode is used a lot so it gets better, but it's still not universal. The worst I have seen is a system that silently removed all non-ASCII characters when entering passwords.