Not fully localized compatible (date_i18n missing in some cases)

Hi.
Thanks for the great plugin.
I tried about the 1.2.3 version with Greek language and noticed that in some places the strftime() is causing display problems. (For example in calendar.class.php line 104 )
I' m in the middle of changing the code in order to use the date_i18n() instead.

If you think it is useful I can Iend the changed files to someone in wpmudev in order to include them in the next version.

Thanks in advance