Is it permissible to pray the 'Isha prayer half an hour before the Fajr athan, given that the time for the 'Isha athan is late in the country where I reside?

The time for the Isha prayer begins when the red twilight disappears and ends at the break of dawn, according to the preponderant opinion.

So, the prayer is valid if performed half an hour before the Fajr adhan, provided that the adhan is called at the break of dawn. However, delaying it past midnight is not permissible without a valid legal excuse.