Hi,
I am having the same issue, I think the translation to French language is not correct, it should be “événement”, not “évènement” as used in the-events-calendar-fr_FR.po, but you’re right in this file we do not have all places where “évènement” is used.
I have the same problem as your using widget but here I was able to force the wording by having in my child theme a custom list-widget.php.
This is just a quick fix for widget, not for all menus, buttons.. hope to get this fixed through a next upgrade.
Gérard.