I am looking for translation of the excerpt: (read more…) but I cannot find it in the ATA template? Do I have to edit a PHP file? Is this a WordPress function outside the Template?

did you try a forum search??
try an advanced search and limit it to the 'Languages & Translations' sub forum

Yes I did and I know where the setting is in ATA but still I get (Read more...) I am using a plugin, so I think the plugin is not looking at the template but getting this <!--more--> from somewhere else maybe directly form wordpress?

I am using tpg-get-posts ( http://wordpress.org/plugins/tpg-get-posts/ ) to get my post under the homepage, then I put this code on my homepage on the bottom:

[tpg_get_posts show_excerpt="true" *mag_layout="true" thumbnail_size="medium"]

show_excerpt="true" shows (Read only...) with a link, but my setting in ATA is:

Lees verder %post-title% (this is Dutch) but both are not seen by the plugin I guess?

So where is the plugin getting the text (Read more...) when I use the <!--more--> tag in my posts?

probably from line 31 of the plugin file class-tpg-gp-admin.php

I found it! more_link_text="My Custom Text"