Event Calendar works fine with Translatable, except when trying to add announcements to the calendar in the second language. When clicking the "add announcement" button, instead of the form there appears the error message:
"I can't handle sub-URLs of a CMSMain object."

When adding announcements manually to the database table CalendarDateTime they are displayed correctly, on the site and in the CMS. However when trying to edit them in the CMS (in the second language) the same "can't handle sub-URLs" error appears.

Tested with:

• SilverStripe-v2.3.2
  
• modules-event_calendar-r51
  
• modules-dataobject_manager-r197

• SilverStripe-v2.3.3
  
• modules-event_calendar-r83
  
• modules-dataobject_manager-r293

I assume this is easy to fix, and then Event Calendar and Translatable can be used together with no more problems.

Almost there:
After applying the patch quick patch for LangSelector() in CMSMain.php the error seems to be gone, even as content_admin, but despite having entered it in the calendar of the second language the announcement is saved in the calendar of the first language, and not in the calendar of the second language.

I have to take that back, now the language selector works fine, but the event calendar still or again gives the error message:
"I can't handle sub-URLs of a CMSMain object." as described above.

UncleCheese, there is a (minor) typo in modules - Revision 83: /trunk/event_calendar/templates/Layout/CalendarEvent.ss
Line 11 is

• <h4><% _t('FILTERCALENDAR','Fitler calendar') %>:</h4>

• <h4><% _t('FILTERCALENDAR','Filter calendar') %>:</h4>

upgraded to modules-dataobject_manager-r295 and the pop-ups are pop-ups again, but the I can't handle sub-URLs of a CMSMain object. error is still there when trying to add announcements in the second language.