Hey Lucas,
thanks, again
Now, my problem is: Entries within my php file are not displayed in the lexicon. Neither are new entries I added from the backend. They are not added to the php file, either. They just exist in the cache file for that topic.
Moreover, I added several languages to that namespace & topic. however, only the English one is displayed. So I can't choose between languages.
Thought maybe it is a file permissions problem. Turned out it isn't.