I installed the thunderbird-langpack-en-GB version 3.1.7-i586-1vl70, which pulled in Thunderbird version 10.0-i586-1vl70. However, the spelling was still US-english (IE, "favorite folder", or the date format of mm/dd/yy), and I couldn't find a way to change this. So I tried installing Thunderbird version 3.1.7-i586-1vl70 first, and then the langpack, but it still came out as US-english. I've subsequently upgraded again to version 10.0-i586-1vl70, and have not yet found a solution to changing the locale setting of Thunderbird. I have edited /etc/profile.d/lang.sh replacing en-US with en-CA, which did change the language settings of some programs (IE, Abiword), but that did not affect Thunderbird.
Note, I’m not talking about the spell check. I did get an extension for that -- Canadian dictionary -- which works. Rather I’m talking about the spelling that’s on Thunderbird itself. So, does anyone know how to get the package thunderbird-langpack-en-GB recognized by Thunderbird?