Here we go. Please give it a try.
This plugin includes the hard translation work done by @DDo! 
https://github.com/gschlager/discourse-german-formal-locale
While creating this plugin I noticed a missing feature in Discourse: The new de_formal locale doesn’t reuse the German locale defaults for site settings. I’ll enhance this in the future.
The translations on Transifex have been moved to Discourse Formal German localization.