glibc will no longer contain pre-generated locales. This means users who use something else than the C locale should take some steps when upgrading to the new glibc-2.3.6-2 package. glibc will try to autodetect the locales needed on your system and enables them in /etc/locale.gen. After this, it will run /usr/sbin/locale-gen. The glibc package will look in the $LANG variable and in /etc/rc.conf for the LOCALE setting. If you use any other locales than these, edit /etc/locale.gen and run /usr/sbin/locale-gen. This should generate all the locales you need. The package is uploaded to testing first, if no bugs are reported, it will go into current quite soon.
For users who have been running 2.3.6-1 from testing, this autodetection won't work, as the /etc/locale.gen included in the package is under pacman's backup control and doesn't contain the required lines to support autodetection.