Geeklog leaves the language and formatting of date and time (mostly) to PHP. For that to work, you have to set the 'locale' entry (see above), so that PHP knows which language to use.
First of all, please double check the correct spelling of the locale setting (mixed lower/upper case, uses an underscore).
If that doesn't work, it's possible that your server doesn't support that locale. Try the little PHP script I posted
over here and see what happens.
bye, Dirk