Update to German locale [de]

[calipo69]

Hello!
I went through the whole German translation, put there the missing parts and changed all files from "2nd person plural" to "2nd person singular". In my opinion it is much better.
Hope I could have helped.
de.txt

Calipo69 from Vienna

[paulrouget]

Thank you so much ❤️ I'll add that to the next release :)