With the localization efforts by the team currently responsible for maps comes increased visibility into the potential languages a map can be presented in. Currently the maps use a set decision tree to determine which language to display labels in. First the wiki language, then fallback languages, then local (geographically speaking) language. What if users of the map could select from a list of languages to render the map tiles in a specific language. Acknowledging, of course, that not every label will be available in every language and that some selections would result in zero visual change.
Provide an interface to allow users to select from a list of languages. This should probably be when a maps is full-screen only as to not clutter the viewport for embedded maps,
When a language is selected, the Wikimedia maps switch the "lang=" attribute to the new language selected. The map is re-rendered with the new language. Labels that are available in the map view are now rendered in the newly selected language.
Optional: provide a way for users to revert the map to the 'default' language setting as when the map was first viewed.
Note: The team currently responsible for maps has a defined scope and timeline. I am not suggesting they prioritize this feature over current work. This task is to document the interest for potential future work.