Hello,

Check if you don't have any other extension that could return this issue by overriding core joomla function to generate month.

As iCagenda is using there Joomla core system to translate months as well as days.

The last time i saw such issue, it was due to another third party extension, but i don't remember which one... (check if same issue with Joomla article date when display enabled in frontend).

Best regards,
Cyril