If you want to know something about card games, you need the web portal "Pagat" - at least that's what Synes Ernst (former chairman of the jury Game of the Year) says in his blog "The Player". Behind "Pagat" is the now 72-year-old British mathematician John McLeod, who has been involved with card games since his studies in Cambridge. The website describes around 500 card games (including variants) from all over the world and is therefore also a treasure trove of research for game designers.

Link to the blog in German language 

Link to PAGAT