I opened https://www.wikidata.org/wiki/Special:NewItem?uselang=de&site=dewiki&page=Pik%20Alexander%20von%20Humboldt&label=Pik%20Alexander%20von%20Humboldt and filled in the field "Beschreibung". The UniversalLanguageSelector was set to "Deutsch" (German).
So the fields were
- Bezeichnung: Pik Alexander von Humboldt
- Beschreibung: Berg im Tian-Shan-Gebirge in Kirgisistan
- Website der ersten verlinkten Seite: dewiki
- Titel der ersten verlinkten Seite: Pik Alexander von Humboldt
After creating the item, the result was this: https://www.wikidata.org/w/index.php?title=Q18778676&oldid=188277395
As you can see there, label ("Bezeichnung") and description ("Beschreibung") were saved in English.
Same happened for another user here: https://www.wikidata.org/w/index.php?title=Q18775638&oldid=188261511
The form was German, but the content (i.e. label and description) was saved as English.
To make it even more confusing, when I tried it before (same procedure as above) with another article, it worked fine (see https://www.wikidata.org/w/index.php?title=Q18778388&oldid=188275504; label and description saved in German).