Add informal German locale

[lislis]

Hey there and thank you for you work on this!

I have a question: I used the German locale provided here as a basis but changed it to use informal 'Du' instead of the formal 'Sie' because it fits the tone of my app better.

I'm interested in contributing this back but I was wondering if this is a case you want to handle at all? How do you handle formal/ informal cases in file naming (if at all)?

Thanks in advance!