Hi @lfedele,
As I started looking at this, I realised that the text should already be translatable using WPML. The string you need to translate will most likely be listed as:
“This content is password protected. To view it please enter your password below:”
If this string is not showing, your theme might be changing it. So you may need to look through the strings to see which one is applicable.
If you then set the message within each of your site’s languages via WPML, it will translate automatically and you won’t need to use this plugin at all.
I hope that helps, but if you have any other questions just let me know.
Phil