hello horst,
in your case for the german language it should be located at administrator/language/de-DE/de-DE.plg_app_user_blog.ini
instead of updating it manually you can also grab the latest files from the easyblog transifex page here: https://opentranslators.transifex.com/projects/p/easyblog/language/de_DE/

just keep in mind that since these app translations and also easyblog fields translations aren't longer part of the easysocial transifex project they are NOT getting installed automatically when you're updating the easysocial languages via the backend. they now have to be handled manually.

hope that helps but if you face any issues feel free to get back to us at any time. have a nice day