Something is going wrong. What I have done is to add the following to the template called "Datei":
<div class="fileinfotpl" style="display:none">
<span class="fileinfotpl_desc">{{{Beschreibung|}}}</span>
<span class="fileinfotpl_date">{{{Datum|}}}</span>
<span class="fileinfotpl_aut">{{{Schöpfer|}}}</span>
</div>
After that I added the template to the file's page, purged it again, edited it a second time to really meet the suggestion of the Q&A section on the help page. However, nothing happens.
Before that I accidentally added the license information to that very template too, but this broke everything. The only thing this proved is that the extension CommonsMetadata is actually trying to fetch something. Because of this I am puzzled that it is not working even though everything was done as instructed.
I am working with MW 1.23.1, MultimediaViewer of 2014-04-22 (e0d3c9e) and CommonsMetadata of 2014-06-03 (6b330e1).