Below reported problem also applies to Turkish translation (search for %l to find all relevant strings)

+++ This bug was initially created as a clone of Bug #648394 +++

The formats string in gnome-shell.po that are supposed to be a 12-hour time format:

#. Translators: This is a time format with date used
#. for AM/PM.
#: ../js/ui/dateMenu.js:177
msgid "%a %b %e, %l:%M:%S %p"
msgstr "%a, %e. %b, %H:%M:%S"

#: ../js/ui/dateMenu.js:178
msgid "%a %b %e, %l:%M %p"
msgstr "%a, %e. %b, %H:%M"

#. Translators: This is a time format without date used
#. for AM/PM.
#: ../js/ui/dateMenu.js:182
msgid "%a %l:%M:%S %p"
msgstr "%a %H:%M:%S"

#: ../js/ui/dateMenu.js:183
msgid "%a %l:%M %p"
msgstr "%a %H:%M"

Are done as straight-up 24-hour time formats. This makes the switch in System Settings that is supposed to switch between 12-hour and 24-hour time do nothing, which looks buggy. 

 https://bugzilla.redhat.com/show_bug.cgi?id=698698

Compare the gnome-panel translation:

#: ../applets/clock/calendar-window.c:316 ../applets/clock/clock.c:448
#: ../applets/clock/clock-location-tile.c:507
msgid "%l:%M %p"
msgstr "%I:%M %p"

Since the default value for the toggle switch is a 24-hour format (for all locales), I don't think it matters that 12-hour time with AM/PM isn't natural in German.