You will find resources for all languages of this challenge here. These are by no means complete or perfect but will hopefully serve as a starting aid.
In case you stumble upon websites or books or other things for your challenge language, and you think that they would help other challengers in the future, please do not hestitate to spam me with whatever you found. I will gladly add it to the resource list for future challenges. Just text me on Twitter, Instagram or mail me.