I installed a multisite + the domain mapping plugin. Afterwards I changed the base domain - via editing all entries in the database.
I know it's perhaps not the best approach but it works perfectly so far.
base domain: webpack.webhost.com
1) domain: webpack.webhost.com/english -> http://www.mydomain.com
2) domain: webpack.webhost.com/deutsch -> http://www.mydomain.de
Only downside of this is that my featured images use the BASE domain as src url...
Thank you in advance!