Just a quick note:
If you really want to delve into software development or even game development, then the best resources are found in English. I myself am from Germany and a software developer (game stuff is just a hobby) and when I compare the resources on the internet, most good informations are found in English (
stackoverflow.com for example is THE site on the internet, where you can find quick help. They have a lot of sub pages for specific topics, like
Game Development).
The books from Packt are available in print and PDF format. Sometimes both is cheaper then just digital
But make sure to work through the SFML tutorial on this site
Anyway, good luck!