Sorry, don't take it personaly. But I'm confused. I will not write 
any testunit. I just report real bug. You don't handle in strftime() 
%-d and %-m, which is on all czech locales, not broken locales, not 
edit locales... PHP strftime() works correctly. See result in my 
attachment. That's all what I say, take it or leave it.  And don't be 
upset :-)

  Regards
  Jiri

Stop spreading FUD. Did you actually take a look at my commit? It's a 
unit test for what you say is supposed to be broken in Horde_Date and 
it passes just fine. If you think Horde is broken then provide a unit 
test that demonstrates that.

  This characters is on ALL systems in Czech. And they are working in 
all programming languages, only Horde has problems. What's wrong witch 
you guys? You want to send this project to bottom? When people sending 
serious bugs you take it as joke? :-(

Horde_Date isn't even using it's own strftime() implementation with 
this format string, because it contains unsupported characters.

Changes have been made in Git for this ticket:

Add unit test for bug #10759.

  1 files changed, 17 insertions(+), 1 deletions(-)
http://git.horde.org/horde-git/-/commit/38f4fb25724f483bc7c296231c0192f1b867192b

This bug appears not only in Date.php, but in lib/Kronlotih.php too.
When adding new event, same error caused by own replacement of strftime.
That? because your are not using system wide strftime.
It? shame do same mistake twice - should be called by Date.php and 
Horde_Date ;-)

Horde in czech has serious problems with own written functions in 
Date.php class Horde_Date.
Functions strftime and _strftime is unable to handle czech locale 
%-d.%-m.%Y, this is not locale problem!
All czech distros uses this, try this:

setlocale(LC_TIME,'cs_CZ.UTF8');
$f =  nl_langinfo(D_FMT);
echo $f." = ".strftime($f,mktime(1,1,1,3,3,1976)). "\n";

Internal strftime function of PHP works fine, but user defined 
function of Horde not. Why you preffer own??!
It's realy not bug in locale as described in #10435

Working pactch is add this line to Nls.php:
self::$_cache['nl_info'][$item] = 
preg_replace('/%-([dm])/','%$1',self::$_cache['nl_info'][$item]);
just before return in getLangInfo($item) - but that not nice patch :-)