Hi. How do i get my son to start speaking? I live in Africa and speech therapists are not available. He is 5yr

My second born son has so far failed to learn how to speak. He only makes the Ku sounds to everything. He can imitate may things like dancing, hand motions, can play computer games, can copy letters and numbers, but he cannot imitate speech. He loses interest very fast when i try to get him to say something. His elder brother is now 8 yrs old and is very vocal. We have very few speech theraphists here i have to struggle with him. Any ideas on how to boost my efforts? The day he will talk will be the best day of my life. Any help out there? Thanks.