Hello!
https://gnupg.org/gph/de/manual/f20.html#AEN33
doesn't seem to have any charset encoding information.
If the charset in the browser isn't set to "western", it won't display
many special characters like "Ä" properly.
In the HTTP inspector I also can't find any encoding info.
Content-Type:"
I just did some more tests. I noticed that if I export the private key
and the certificates contained in the (non-distributable) p12 file with
the following commands
openssl pkcs12 -nokeys -in client.p12 > certs.pem
openssl pkcs12 -nocerts -in client.p12 > keys.pem
and then create an new p12 file