Yeah, I think something on Nostr would be great. It would provide an ability to verify that Lightning is accepted in advance and a way for local businesses to efficiently market and communicate. Having localization is great, but I don't think should need to be a localized app.
Discussion
If well known, I think we already reached a point of possible bitcoin tourism. Aka, bitcoiners who would love to visit places just to experience some irl usecases of bitcoin beyond internet use.
As you mentioned, yes it would be great to be able know in advance. And I think at least some would consider it in their trip plans. :)