Change Text "Select a category" in Woocommerce Product Widget

Sorry to bother, i’m currently navigating the various .php files but couldn’t come out with any solution on this one, and some others too, but this particular one is more pressing at the moment.

I added the nice Product Categories Widget on my sidebar
on https://www.provista.it . As you can see my site isn’t in English so i had to translate many functions and stuff.
Now i need to change the placeholder text of the widget from “Select a category” to something else. No luck from
class-wc-widget-product-categories.php
nor from
class-product-cat-list-walker.php

Thanks for your support