Good evening Philippe and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the language selection menu disappearing on all events pages.
I would love to help you with this topic.
First and foremost, just to clarify, WPML is compatible with the Events Calendar and the Events Calendar Pro.
The only thing that is not at this point are recurring events. But that will change very soon.
As a first troubleshooting step, could you please provide us with your complete system information in a private reply using the instructions found in the following link?
https://theeventscalendar.com/knowledgebase/sharing-sys-info/
Secondly, can you confirm if you already went through the following documentation on how to use WPML alongside the Events Calendar ?
https://theeventscalendar.com/?post_type%5B%5D=documentation&post_type%5B%5D=tribe-knowledgebase&s=wpml&submit=Filter
Have a good week-end,
Geoff B.