Dedoimedo posted a short tutorial explaining how to fix language, date and other regional/locale settings in Ubuntu family installations

The problem you're facing is as follows. You installed Ubuntu or Xubuntu or one of the other flavors, and during the installation, you chose English as your preferred language. However, after the installation, you notice that the system date shows in a non-English format or even a foreign language that matches the region you're in. Likewise, in the terminal, date & time stamps on files when running the 'ls' command are also encoded in another language. Not what you expected.

I will show you how you can fix the problem. This has to do with the locale, and we will remedy the problem so you can enjoy a single language of your choice for all menus and options and tools, regardless of the geographical location. This tutorial refers to the recent Ubuntu releases, all of them, including Linux Mint. In fact, I'm going to demonstrate using the latest Olivia release. Follow me.

  How to fix language and date settings in Ubuntu family