Reading through John Wayne’s list, he’s the leading man every damned time.
Most everyone else known as being prolific - Lee, Michael Caine, and the like - were prolific by accepting supporting roles. Michael Caine is usually a supporting player.
But John Wayne was always the star. Hell, he was more than a star - he was a brand.
Not only do I think Wayne holds the Engish-speaking, non-porn record, I think he always will. The nature of movies today precludes one person starring in that many Hollywood films. Wayne for much of his career was putting out a new movie every two MONTHS. Here, year by year, is his credit count for a random chosen chunk of his career:
1935 - Eight movies
1936 - Seven movies
1937 - Five
1938 - Four
1939 - Six (incl “Stagecoach”)
1940 - Four
… and so on. He slowed downa bit more after the war, likely just because movies got more elaborate and took longer to make, but was still phenomenally prolific. Wayne made 20 feature films in the 1950s, some of them classics like “The Searchers” and “Rio Bravo.”
By comparison, Will Smith, who is about as one-name-brand a movie star as you can hire today, has appeared in only 18 full length motion pictures in 18 years, and a few of those are supporting roles and one of them was an animated film. Brad Pitt had been in 37 feature films (by my count; I’m doing this quick off IMDB) in about 20 years, which by modern standards is quite prolific for a superstar, but about half are supporting roles.