After updating to glibc 2.19-1 today, many programs started to crash in locale-related functions. For example:

pacman -Qs test (crashes in towlower())
thunar (crashes in __collidx_table_lookup())
mousepad (crashes in __collidx_table_lookup())

I think I tried rebooting and it didn’t help, but I’m not 100% sure of this.

Downgrading to glibc 2.18-12 and running locale-gen fixed the problems.
The packages I had to downgrade to were:
binutils-2.24-2 [removal] binutils-multilib-2.24-1
gcc-go-multilib-4.8.2-7 gcc-libs-multilib-4.8.2-7
gcc-multilib-4.8.2-7 glibc-2.18-12 lib32-gcc-libs-4.8.2-7
valgrind-3.9.0-1

I’ve seen  FS#38840  that mentions a similar crash caused by not running locale-gen, but in my case locale-gen was run automatically after the update to glibc 2.19-1 and I didn’t change the locale afterwards. I haven’t tried re-running locale-gen manually just after pacman -Syu.

The enabled/generated locales on my system are:
en_GB.UTF-8
en_US.UTF-8
fr_FR.UTF-8

And the current locale:
LANG=en_GB.UTF-8
LC_CTYPE="en_GB.UTF-8"
LC_NUMERIC="en_GB.UTF-8"
LC_TIME="en_GB.UTF-8"
LC_COLLATE="en_GB.UTF-8"
LC_MONETARY="en_GB.UTF-8"
LC_MESSAGES="en_GB.UTF-8"
LC_PAPER="en_GB.UTF-8"
LC_NAME="en_GB.UTF-8"
LC_ADDRESS="en_GB.UTF-8"
LC_TELEPHONE="en_GB.UTF-8"
LC_MEASUREMENT="en_GB.UTF-8"
LC_IDENTIFICATION="en_GB.UTF-8"
LC_ALL=

I’ve attached the relevant pacman.log lines for the update that caused the problem.