The map was interesting but it just got me wanting the whole list which is on the openculture post but not on the reddit link. So I think it adds more than just "blogspam" to the original source (but probably not much except for the list).

You're right, that does appear to be the primary source. It's a Redditor called Fummy who creates various maps:

https://www.reddit.com/user/Fummy/submitted/

Fummy has created a new version that corrects the colors for the rankings (so that red is now the most difficult, green is easier), updated the data on language difficulty, and wisely added their Reddit user link to the new image:

https://i.imgur.com/37xlzKE.png