ALL his "sounds" are a "precursor" to talking.
So don't worry.
He is young.
Is his Ped worried? If not don't worry.
Boys, are generally later with talking.
It has nothing to do with them understanding.... even if they understand everything, it doesn't mean something is off with them, just because they don't 'talk' yet.
Einstein... did not even talk until 3 years old. And he was a Genius!
And, the 'articulation' and pronounciation of words, are not perfect yet.. .they are STILL needing to get their mouth motor-skills in line... it is in the p.r.o.c.e.s.s of developing. Talking... takes mouth/tongue/lips/throat coordination.
My son, had speech therapy from 19 months old until almost 3 years old. They gave him an overall developmental assessment and he was even "advanced' in several areas for his age. Just talking, he was "late." Not anything wrong with him clinically, he was just not ready, nor his coordination of his mouth yet. But the speech therapy DOES and DID help. It was free, that is why I did it and I believe early intervention helps. Every state, has an "Early Intervention" program to address speech and other developmental concerns. In my state, they are really great.
Ask you Pediatrician about it. You don't have to be referred, at least in my State. I just signed up myself.
Even with reading, talking a lot to him etc., if the child is not ready nor able to talk... it will take time. But whatever you do, do NOT "force" it or make him feel odd about it or that you are disappointed in him. That will not encourage the child.
all the best,