Novice question: debugging a package fix: can I locally override just a single line of a long multi-line string in a package?

that did it! even with test I can finally see the installPhase run (and the error trigger)

Ah, no: the reason for this change is because I’m 99% sure the CLI parsing of the command being called is not happy with space-delimited arguments on flags. That is: its CLI parsing is implemented such that it expects --a=b not --a b, thus the current script’s way (of passing in --locale into it) can never work. See this writeup: