I have an update :
after making sure i was using the right .po in the right folder
that is was translated or that I translated it myself
that the .po was updated according to the latest .pot (repair the .pot before update the .po if broken)
I forgot to delete the /wp-content/language/plugin folder to reset cache.
Once i did that, almost everything works BUT “event category” on the filter bar (see previous screenshots)