Thank you for contacting us.
Please, try to download from here: www.jomsocial.com/translations/translations/de-DE
You install it just like any other Joomla! extension - via Joomla! installer.
Make sure that you set German as default language for backend.
If it still doesn't work, please, read this blog post: www.jomsocial.com/blog/j37-translations
thanx a lot. Installing works. But Guru remains English. With other components I have no problems. Funny. Use Joomla 3.6.5
great. 1000 thanks! The backend is now in german.
For frontend translation I must use Settings> Languages or is there a language file too?