What is the ruling on someone who fasted the first day of Ramadan with a country that did not declare fasting, and should he complete it with his own country if it fasts 30 days, or with the country he fasted with?

The preponderant opinion is to consider the divergence of moon sighting horizons. If a person's horizon differs from the horizon of the country with which he fasted, he should continue fasting with the people of his country, even if he fasts for 31 days. However, if he adopts the view that the divergence of horizons is not to be considered, there is no objection to him fasting and breaking his fast with a country other than his own, but he should conceal this if it would lead to discord or strife.