Hello Roberto,
I've done a few other changes to fix this weird issue with Ajax and current language.
One pro user had it too on a site where i don't have the issue, and the strange thing is that this user has the issue only on one computer (other computer with same browser and same site does not have it).
On my side, after multiple test, i was able to get this issue only on 1 of 5 test sites where i've tried to reproduce it.
So, mainly issue comes from language cache system of Joomla or something related, and current language can't be get in a Ajax request in some cases (mysterious issue).
Here a new version, full package, as other changes added in iCagenda library to improve the correct detection of the current language by passing the lang to the Ajax data directly. So, many changes here and there.
Could you install this dev version, and check if all is ok, and if any issue left, to give me more details (for example, does events have language set on it/en or on all "*" and what is the settings in the module for the "Routing" options: " Parent List of Events " and " Use Menu Filters " options.)
Thank you!
Cyril