How can one repent of cursing the people of an entire country, and will Allah forgive that given the impossibility of asking their forgiveness, and will supplicating for them erase the sin according to the Hadith: "And follow up a bad deed with a good deed which will wipe it out," and will Allah not forgive these sins except through seeking absolution?

Cursing is not among the ethics of a Muslim, and one must guard their tongue from it and from every obscene word, as the Prophet, peace and blessings be upon him, said: "The believer is not a slanderer, nor a curser, nor an obscenity speaker, nor an ill-peaker." It is not permissible to curse a specific person unjustly, nor to curse the people of a country in general. Repentance from cursing the people of a country, like repentance from all other sins between the servant and their Lord, is achieved by regretting, ceasing, and resolving not to return to it. If you seek forgiveness for the people of that country and supplicate for them, you have done well.