What are the consequences for someone who cursed the mother of his colleague with an abusive word in a language other than his own, then repented years later, and does the right of the offended person lapse due to his indifference?

Accusing someone of zina (fornication/adultery) or sodomy is forbidden and a major sin. Such an accusation can be made in languages other than Arabic, through understandable gestures, or in writing, provided the accuser is an adult, of sound mind, and understands the meaning.

If a person accuses a mother or a man's mother of zina, the right to demand the prescribed punishment (hadd) belongs to the mother, and it is not carried out unless she requests it. If the mother is deceased, the right devolves to her son, who can then demand it and have the punishment carried out.

Repentance for making such an accusation does not require informing the accused, as informing them would cause them distress and stir up animosity. Rather, the repentant person should seek Allah's forgiveness, supplicate for the accused, and mention their good qualities in the contexts where they slandered them.