Final answer:
The Sotho-language novel about the Zulu king published in 1925 is "Chaka" written by Thomas Mofolo.
Step-by-step explanation:
The Sotho-language novel you're referring to is "Chaka" by Thomas Mofolo. It was indeed published in 1925 and is an imaginative retelling of the life of the early nineteenth-century Zulu king, Shaka Zulu. This novel has been recognized as not only a significant work of African literature but also as a pioneering piece in the effort to reclaim African history from the colonial narratives that often suppressed it. Mofolo's novel represents one of the early instances in which African writers sought to celebrate African culture and history through literature.