You didn't quite get what I was trying to say or I explained it poorly. It's probably the latter.
The problem isn't about the client knowing your location or language. Instead, it's about the other users knowing that information about you.
If you have your browser set to French and the #nostr client uses that information to automatically share your notes with other French users, this reveals your language and country to those users, even if your notes are in English.
It's a #privacy hole that could be exploited by an attacker to help deanonymize the country/language a specific user if they have this knowledge and are willing to put in the effort.