Train on java compiled to class files. Then go from class back to java.
Or even:
Train java compiled to class files, and have separate models that train from Clojure to class and Scala to class files. Then see if you can find some crufty (but important) old java project and go: crufty java -> class -> Clojure (or Scala).
If you could do the same with source -> machine instructions, maybe COBAL to C++! or whatever.
LLM source recovery from binaries is thing. The amazing part is that they are pretty good at adding back meaningful variable names to the generated source code.
AI cannot even lint properly right now and you want it to decompile? good luck, there's too much hype going on people really think this is possible this year?
In the end always remember it's just autocomplete, it's pretty terrible at translations that are not natural language to natural language. I worked on a natural language to SQL and it was impossible to make it consistently generate valid SQL for Postgres, and I'm talking about natural language to SQL not virtual machine instructions...