If I (a British speaker) am in your country (which uses 1st, 2nd 3rd; not G, 1st, 2nd) Then I would adapt to your system, and say, in perfect British English "I live on the second floor". Because in your country "second floor" means up one from the ground.

So I'd say "I live on the second floor, please press 2 for me."

I'd expect an American, visiting the UK to use the British numbering of floors if they are in a building that has a "Ground floor". The system of naming floors is just a system of names, it doesn't really depend on dialect.

There could be some situations in which I'd need to clarify but they'd be pretty rare. I might sometimes get confused and make mistake, but that is also not a problem.

If I (a British speaker) am in your country (which uses 1st, 2nd 3rd; not G, 1st, 2nd) Then I would adapt to your system, and say, in perfect British English "I live on the second floor". Because in your country "second floor" means up one from the ground.

So I'd say "I live on the second floor, please press 2 for me." And likewise I'd call the ground floor "the first floor".

I'd expect an American, visiting the UK to use the British numbering of floors if they are in a building that has a "Ground floor". The system of naming floors is just a system of names, it doesn't really depend on dialect.

There could be some situations in which I'd need to clarify but they'd be pretty rare. I might sometimes get confused and make mistake, but that is also not a problem.

If I (a British speaker) am in your country (which uses 1st, 2nd 3rd; not G, 1st, 2nd) Then I would adapt to your system, and say, in perfect British English "I live on the second floor". Because in your country "second floor" means up one from the ground.

I'd expect an American, visiting the UK to use the British numbering of floors if they are in a building that has a "Ground floor". The system of naming floors is just a system of names, it doesn't really depend on dialect.

There could be some situations in which I'd need to clarify but they'd be pretty rare. I might sometimes get confused and make mistake, but that is also not a problem.

If I (a British speaker) am in your country (which uses 1st, 2nd 3rd; not G, 1st, 2nd) Then I would adapt to your system, and say, in perfect British English "I live on the second floor". Because in your country "second floor" means up one from the ground.

So I'd say "I live on the second floor, please press 2 for me."

I'd expect an American, visiting the UK to use the British numbering of floors if they are in a building that has a "Ground floor". The system of naming floors is just a system of names, it doesn't really depend on dialect.

There could be some situations in which I'd need to clarify but they'd be pretty rare. I might sometimes get confused and make mistake, but that is also not a problem.