Curious that Geronimo and all the Apache only speak Spanish. It comes across as not genuine, and as noted there's no evidence Geronimo spoke Spanish. My guess is that the producers had too hard a time finding actors who could speak in a native American language, specifically Apache. So Spanish became the substitute Indian language.
shareAfter centuries of contact with Spanish and Mexicans in the southwest USA a lot of Apaches knew enough Spanish to use Spanish names in addition to their Apache names. In many places and eras people had to know two or more languages. Americans are rather unusual in mostly speaking only English, so you are imagining that the Apaches were like Americans and only spoke one language.
In 1873, when the Tonto Apaches and the Yavapais surrendered to General Crook at Camp Verde, their spokesman Chalipan was quoted as saying said they did not surrender because they loved the general, but because the general had "demasiado cartouches de cobre", Spanish for too many copper cartridges, showing that Chalipan spoke Spanish as well as Apache and Yavapai.
Most Apaches only had an Apache name but many famous ones also had Spanish names.
Geronimo "Jerome"
Victorio "Victory"
Mangus Coloradas "Red Sleeves"
Mangus "Sleeves"
Miguel "Michael"
Cuchilo Negro "Black Knife"
Loco "Crazy"
Diablo "Devil"
Nana "Grandmother"
etc.