Which countries are the most accepting towards nudism?
France is a good destination for nudists - but only if you stay in the nudist resorts. Nudity away from such places is most definitely frowned upon. In that respect, Spain is better, as the freedom to be naked is more widespread, especially on their beaches and often in the countryside around in my experience. For nudity in mountain areas, Austria is probably one of the best, but I have no personal experience there.
I would describe the Nordic countries (Denmark, Finland, Sweden, Norway along with Iceland and Greenland) as pro-nudity but anti-nudist in terms of social nudity. If you have a group of friends and meet regularly to share naked saunas, it's deeply ingrained in the culture. However, friendships are very selective and people are reserved. What's the biggest problem Nordics would have going to a nudist resort? Is it that someone might recognize them and see them naked? Nope. It's that they might need to have to talk with a stranger. Naked or clothed, that keeps them at home.
Countries in Western Europe have more nude friendly people and places compared to the the US, I think. Spain provided me with lots of nude opportunities along the Mediterranean. One day maybe I will get to Canary Islands.