Hi Klas
This was my first reaction naturally. But if you perform a search in all the *.ini files of the project, looking for 'Today' you will get:
./administrator/language/en-GB/en-GB.com_finder.ini
./administrator/language/en-GB/en-GB.plg_cck_field_calendar.ini
./administrator/language/en-GB/en-GB.lib_joomla.ini
./administrator/language/en-GB/en-GB.com_cck.ini
./language/en-GB/en-GB.com_cck_default.ini
./language/en-GB/en-GB.lib_joomla.ini
and even if you find this string ('today') in ./administrator/language/en-GB/en-GB.lib_joomla.ini and ./language/en-GB/en-GB.lib_joomla.ini, changing the value of JLIB_HTML_BEHAVIOR_TODAY has no effect on the frontend.
Thanks
Cyril