There is no way to configure this text in the control panel, but if you are using a custom theme then you can modify the code in one of the theme files to change this text. Specifically, you would need to change line 2 of the _flash.html file. That file likely will not show up in the "Files" tab of your theme, as it is hidden by default, but you can get it to show up by creating a new file (using the "New File" tab) and naming it "_flash.html".  It will then show up and can be edited.

Line 2 will look like this:

<div class="flash-message">{{ flash.message }}</div>

But you can change it, like this:

<div class="flash-message">{{ flash.message | replace: 'Thanks for your interest','Gracias por su participacion!' }}</div>