When I was learning origami, before the internet was available, the few books I could find beyond basic ones in English were all entirely in Japanese. You can get very far with just the diagrams even for complicated geometries, though it takes a good amount of trial and error and effort. However nowadays I can simply use my phone's Google Translate camera to see the translations superimposed on the image itself!

I haven't done much since I was a teenager, but once you have a feel for the basics, even non-standard diagrams are plenty to learn a new pattern. It seems so complicated, but most origami comes down to just a handful of techniques. That's one of the coolest things about the art, imo. There may be 100 steps, but those steps are all variations on a few different folds.