I have created a prototype for the proposed fix here:

https://github.com/carmenbianca/argparse

I'm not a regular Python contributor, so I simply copied argparse.py out of Lib and started working on my own copy.

The changes are, all things considered, not very big. But it would add a `locale` directory in Lib, which I'm not sure is okay or not.

There would also need to be a mechanism in the build process that puts the compiled MO files in Lib/locale/*language*/LC_MESSAGES/argparse.mo.