hi,
in your latest version "com_easyblog_pro_3.9.16263" you have commented out the logo code line in the email template. it looks like there is something in progress with this line or do i miss here something?
email.template.html on line 31

<!-- <img src="<?php echo $logo;?>" /> -->

also when i remove the html comments, this php code does not bring the logo up in the emails.
the output in the mails are a empty IMG Tag:

<img src="" />

i do not know why but does not working.

also in the german transifex language file you have forgotten to add the email template titles:
example:
COM_EASYBLOG_NOTIFICATION_NEW_BLOG_POST
COM_EASYBLOG_NOTIFICATION_NEW_COMMENT
and so on ... please add:
https://opentranslators.transifex.com/projects/p/easyblog/translate/#de_DE/frontend/