Thanks, this will be useful for many languages. Unfortunately not for German, the spelling reform of 1996 prevents us from using any public domain texts.
Feel free to transfer the text to your needs (or sc critera).
It is Public domain. 
I searched for an automatic spelling converter for this reform a while ago, but I couldnât find anything. Just replacing single words like âdaĂâ -> âdassâ wouldnât be enough and lead to sentences with mixed old and new spelling.
Found this:
Search for âDer Korrektorâ plugin from Duden Verlag.
On www.chip.de download ( 30 days trial) for open/libre office possible
Did you try double machine translation?
There are also solutions for companies (newspapers)
Programs with defined text rules to apply on text files
(Changing text to new german grammar rules)
without opening them, combining and splitting text files, server integration for every employee etcâŠ
But those are not free and for using them you have to pay big bucks (or Euros in this case).