I just realized that this can provide a definitive answer for the oft-asked question, Is the Masuda Method based on the language played ingame, or the region of the game cart itself?
After hatching a Masuda shiny using the rng method, reset and swap the parents for two pokemon of different languages but same region. If the pokemon is no longer shiny, the Masuda method is based on region. If the pokemon remains shiny, reset and swap the parents for two local pokemon. If the pokemon is no longer shiny, then the Masuda method is based on language.
You can be sure that I'll be trying this out if I ever hatch a shiny (I wish). In the meantime, if anyone else does hatch a shiny, make sure to test this out.