How to change default date language?

[shawn_a]

yeah but that all depends on your host, you need to know what your locales are , which is another issue entirely.
for example i am on windows, so i have no UTF locale support, and i have no idea why i have to use pl-PL instead of pl_PL

It looks like we will have add some iconv conversions to core for locales.
for example on windows
polish is available as Polish_Poland.1250
which can be handled via
echo iconv('windows-1250', 'UTF-8', strftime('%Y. %B %d. %A')) , "<br/>";
for example.
giving us
2014. październik 29. środa instead of
2014. paŸdziernik 29. œroda