Hi Jaako,
Thanks for reaching out, and I’m sorry you’re running into this issue…unfortunately, while The Events Calendar and Events Calendar Pro both currently support WPML, our other plugins like Event Tickets Plus do not (please see this article on getting setup with WPML). Sorry for the bad news! However, we are currently working on expanding support for WPML and hope to release some new functionality later this year, although I cannot make any guarantees on timelines.
We do have somewhat of a workaround for this issue – this post has some steps you can follow to get the tickets to reappear.
I’m sorry I don’t have a better answer for you here, but I hope this helps! Please let me know if you have any questions!
Thanks,
Jennifer