Josh Speaks English,but Also Learned Choctaw from His Grandmother

Josh speaks English,but also learned Choctaw from his grandmother.She grew up on a reservation,but now she lives with Josh and his parents.His parents do not speak Choctaw,though Josh's dad learned Choctaw as a child.Josh's parents believe it's important for Josh to assimilate into mainstream culture and leave the heritage language and culture behind.
Why should Josh be encouraged to maintain the heritage language he's learning from his grandmother? Present a persuasive case that someone might deliver to Josh's parents to convince them that Josh should maintain his Choctaw heritage language.