Comment # 1 on bug 1008951 from Jiri Slaby

diff of non-/working /usr/share/X11/locale/locale.dir:
@@ -346,7 +347,7 @@
 en_US.UTF-8/XLC_LOCALE                 ca_ES.UTF-8
 en_US.UTF-8/XLC_LOCALE                 ca_FR.UTF-8
 en_US.UTF-8/XLC_LOCALE                 ca_IT.UTF-8
-en_US.UTF-8/XLC_LOCALE                 cs_CZ.UTF-8
+cs_CZ.UTF-8/XLC_LOCALE                 cs_CZ.UTF-8
 en_US.UTF-8/XLC_LOCALE                 cy_GB.UTF-8
 en_US.UTF-8/XLC_LOCALE                 cs_CZ.UTF-8 # <--- here again
 en_US.UTF-8/XLC_LOCALE                 da_DK.UTF-8
@@ -864,7 +867,7 @@
 en_US.UTF-8/XLC_LOCALE:                        ca_ES.UTF-8
 en_US.UTF-8/XLC_LOCALE:                        ca_FR.UTF-8
 en_US.UTF-8/XLC_LOCALE:                        ca_IT.UTF-8
-en_US.UTF-8/XLC_LOCALE:                        cs_CZ.UTF-8
+cs_CZ.UTF-8/XLC_LOCALE:                        cs_CZ.UTF-8
 en_US.UTF-8/XLC_LOCALE:                        cy_GB.UTF-8
 en_US.UTF-8/XLC_LOCALE:                        cs_CZ.UTF-8 # <--- here again
 en_US.UTF-8/XLC_LOCALE:                        da_DK.UTF-8

This is the bug. Commenting out the lines makes it working. Note that the lines
en_US->cs_CZ lines are in locale.dir twice (see above).