Although an interesting and constructive discussion about translations in Plone has been started which was overdue I want to come back to my original topic.
In Plone 4 I handled the missing translation of contact-info by customizing the contact-info template in portal_skins/plone_templates - I just hardcoded the german translation there.
I know this is very dirty and not best practice at all, but it worked 
In Plone 5 there is no such template, at least I can't find it in ZMI.
Are there any hints how I can solve this issue until the official translation has been released? Thanks!