Ok, thank you.
The workflow is called Leo Dictionary and you can find it on https://github.com/psistorm/alfredapp
What I figured out so far:
The Script Filter is using a script leo.php
leo.php is using a function toxml() of workflow.php to generate an XML file
toxml() is mainly generating an item list
Alfred comes with an Advanced Script Filters example workflow and the script filter called xvar is giving an example of how to work with variables
==> In my opinion it should work if the toxml() function will be extended in such a way, that it also puts the variable I need into the XML file. This would be a kind of dirty approach but on the other hand the Leo workflow is not under development anymore and XML is deprecated. So, it would not make to much sense to put a lot of effort into changes.
I do not know PHP neither but I have the impression this "hack" could not to be that complicated