Updated: October 5, 2013
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.
You will see the problem in several places. For example, the date applet. The expected English date might be in Russian, Hebrew, Arabic, Chinese, or other languages. Likewise, in the terminal. What we have is a bad date, Indiana Jones reference, funny.
Indeed, you might be tempted to resolve the problem by burrowing into the system settings, but you will all too soon discover that all menu options are properly set and ticked. Moreover, you have explicitly set English during the installation.
No, what you need to do is open a file in text editor: /etc/default/locale. In this file, you will find numerous LC_ environment variable set, so they are defined every time a new shell is started, including your desktop session. Here, for example, I have a Hebrew example, with he_IL encoding instead of en_US.
To resolve the problem, simply changed <lang>.UTF-8 to en_US.UTF-8 or any other language encoding of your choice. Then, save the file, log out and log back into your session. And Bob's your uncle.
This is a fairly trivial tutorial. I am still wondering why the Ubuntu team chose to force locale despite the obvious selection of the language in the installer settings. I mean, if someone wants to use English for their language and keyboard, all options should be set accordingly, or at least an alternative suggestion proposed to the user. But not done behind their back.
However, here's the quick fix you want and need, and no more bad or strange characters that might make you wonder if you've gone ever so slightly loony. Well, as always, you learn something new. So now you have an easy way of controlling your regional settings by fiddling with a locale configuration file. And you also learned about the LC variables. That's winning in my vocabulary.