Whether the following information is complete or entirely correct or contains redundancies I will leave for others to comment upon. In the end, to completely install a working UTF-8 locale from a customized source file in /usr/share/i18n/locales on both CentOS-5 and CentOS-6 I had to do this:

localedef --replace -c -f UTF-8 -i /usr/share/i18n/locales/en_CA@yyyy-mmm-dd en_CA@yyyy-mmm-dd.utf8 localedef --no-archive -c -f UTF-8 -i /usr/share/i18n/locales/en_CA@yyyy-mmm-dd en_CA@yyyy-mmm-dd.utf-8 localedef --no-archive -c -f UTF-8 -i /usr/share/i18n/locales/en_CA@yyyy-mmm-dd en_CA@yyyy-mmm-dd.UTF8 localedef --no-archive -c -f UTF-8 -i /usr/share/i18n/locales/en_CA@yyyy-mmm-dd en_CA@yyyy-mmm-dd.UTF-8 localedef --no-archive -c -f UTF-8 -i /usr/share/i18n/locales/en_CA@yyyy-mmm-dd en_CA@yyyy-mmm-dd

Evidently, the archived version is expected to have the extension .utf8 but all the other aliased extensions are customarily expected as well. I was unable to find where on the system said locale aliases are kept however. The most likely candidate that I found was /usr/share/X11/locale/locale.alias but I could find no entries therein pertaining to my customized locales.

I would like to know the exact location where locale aliases are stored on CentOS systems if someone in the know would share that information.