Hi Daniel,
this happens if you do not have write-access to the openlca.ini file, which is in the same folder as openlca.exe, e.g. if you install as an admin, and use as a normal user. You can then open the ini file as admin, edit, and save, or start openLCA as admin and change the language then. To change the ini file, find
-nl
en
and change to
-nl
de
Hope this helps!
Andreas