change Wiki language or Server App language

Hello, is there a simple way to change the Wiki language or Server App language?

1)

The system OS X 10.10.5 is runs in german and the Server 4 App automatically too.

I want to keep the language german for the OS X System and the Server App.

Only the Wiki should be in english.

2)

The master solution would be if each Wiki user could select his own language.

3)

Further I would like to know if its possible to change each language independently:

system language

server app language

wiki language

Thank you in advance to everyone.

Chris