Right. Decompilation with ASR should be relatively easy and more faithful than average decompilation (though, as mentioned by another commenter, the very-long-term value of decompilation in general is debatable in the face of rising AI like CoPilot).

How do you manage to do that for Python AND Fortran in the same language?

By being a superset of Fortran and subset of Python. It turns out the features map on each other almost 1:1, and the differences can be taken care of by the respective frontends, so the abstracted ASR maps perfectly.