Adobe Acrobat 2015 DC

He everybody,

we try to install the german Version of Acrobat 2015.

If i start the Setup is all german, but i cant Change the GUI-Language in the custom-install-menue. I can only choice "Englisch"

I try to start the Setup with the Parameter "--Installlanganguage=de_DE". But, when i enter the Serial, the Setup says, that is an invalid key. When i use the Parameter LANG_LIST=ALL, i can enter the Serial, but dont Change the language.

I try also, to Change the preferences in Acrobet itselfs, but, any choice is english.

I try the Change the registry-keys, but nothing Change the language.

anybody an idea?

many thx

Robert