There are new German (de-DE, de-AT, de-CH) dictionary extensions available (version 2017.01.12). Please update the dictionaries for LibreOffice:
Would it be still possible to integrate the new dictionaries in the upcoming 5.3 release?
@Andras, like for the last dictionary update, I felt free to put you as assignee to this bug. Please feel free to remove yourself if you don't want to take this. Thanks in advance!