This is not a major bug. It's easy to fix, but it's something I think should be done automatically during the install.
When I install (using MATE 32 bit version of Mint 14 on my netbook), I get the error
language en_GB does not exist using system default
Changing the session default language to British English in the login screen sorted it.
What I was hoping here is for someone to fix it so I don't need to do this.