Good evening Renaud and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the issues you have bumped into while using our Calendar with Polylang Pro.
Truth be told, we are just about to run some tests to validate Polylang Pro’s compatibility with our plugins.
I know for a fact that we collaborated with their team recently to help make this a reality.
As a result, they have announced compatibility on their end as of version 2.2 of their plugin.
At this point, your best guess is to reach out to them to validate the configuration they recommend for this.
Best regards,
Geoff B.