I understand the international nature. But English is very much the language of the world and outside of Lemmy I have found zero sources to support a 19th century use of Libertarianism or Libertarian in any formal manner. I've seen a lot of Mutualist and Anarchist.

Unless you have sources where they actually label themselves libertarians, as in "call me a libertarian", (like they do for anarchist) then all the of internationalism in the world doesn't matter.

There are writers and thinkers from the early to mid 20th century that claim libertarianism. And that's generally an attempt to unify the 10 different kinds of anti statist leftists that exist at the end of the 19th century. Both the pages available for Libertarian Communists, and Libertarian Socialists identify roots in the 1800's, but do not claim their ideology actually started in the 1800s. And it only takes a look at the writers they claim originated them to see they were writing from about 1910 to 1950.

This isn't some semantic thing. Some people want to believe libertarianism came from the first international itself, but from what I've read Proudhon never identified as a libertarian.

Understanding where ideologies have been and where they're going is really important. So people trying to muddle the waters to claim some kind of moral superiority is dangerous and a sign of someone bound more by rhetoric than facts.