Ajax success message filter

First of all thanks for ninja forms, I think it is the most versatile form plugin for WP.

I would like to translate the success message (notification) that I entered into the form’s settings. I was able to do that with a general content filter but it doesn’t work when the form is set to Ajax mode.

Basically I would like to modify what’s displayed in the success message but I cannot find the right way to do this.

Any hint what function/action/filter or other should be used?

https://www.ads-software.com/plugins/ninja-forms/