The only app I've seen thus far that does this is AutoFreeWifi. Its French description got me curious, so I searched for "FreeWifi" and found it was some service provided by Free, a French ISP.

So, really, the French description implicitly tells me that I'd have no use for it outside of France (mind, this would've been fun if it was in Québécois French...).

However, it would save time if in debian/control:
Description: Description in English, saying this has no use for people outside France
XB-Description-fr_FR: French description

Since I appear to be contradicting and confusing myself: I don't mind the main description in another language because it signifies it's not for me, but bonus points if you are courteous and include a small English description saying it'll probably be of no use to you.