this is a common enough question, and enough people want this behavior, that argparse should supply it.

I'm imagining that:  

   type='bool'

would be fine for triggering this behavior, instead of the shadowing that could happen with:

   type=bool

so if type='bool' is supplied, the following things would happen:

 * argparse could use strtobool to interpret the incoming string
 * the default metavar would look something like "{true,false}"
 * followon packages like argcomplete could enumerate the range of different values that strtobool accepts

This is still english-specific -- but it's because strtobool is english-specific, and fixes in strtobool would automatically fix type='bool' here.