Good evening Carlos and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the translations breaking after the update.
I would love to help you with this topic.
Before we begin, just to set expectations, we actually do not support Polylang as multi-language site with our plugins.
That being said, some of our users have achieved some level of success with it (such as yourself).
For multi-language site, we are already compatible with WPML for the Events Calendar free and the Events Calendar PRO. We are also working hard at increasing that compatibility for all of our products this year.
Back to your specific issue, understanding we do not support Polylang, I think you might need to refresh the strings you are trying to translate (since there were changes). If you need to, you can find, the latest version of our strings here: http://translations.theeventscalendar.com/projects
Another possible reason, if your custom translations were found in the /lang/ folder of our plugins, is that they were overwritten by the update.
The good news is that with 4.2 you can now prevent this from happening by storing your custom language files in your /wp-content/languages/ folder
I wish I had a better answer for you, but for now it’s the best one I have.
Let me know how that goes.
Best regards,
Geoff B.