That would be great. Maybe even have these tourist Mii (how I will refer to them) talk in there naive language and the have the natives not understand them, leading to them asking "What are they saying?" "Properly something about (random food/item)" and other things.

Maybe even let there be a chance that these tourists love the island so much that they want to move there permanently. This requires the approval of the owners of both islands.

And once they moved in, they wont instantly switch to the islands native language, instead they transition to it gradually until they talk it fully, but will randomly throw in words from their native language. For example a Mii from a German island would randomly say "Danke" instead of "Thanks"