My DS didn't babble, late to wave too, it was like he was taking it all in. He didn't really say anything until 2.5 and we started to get advice . He is absolutely fine now age 5.5 in year one.
Honestly I went on a course and they said whilst some children need it to be spoke to really simply to encourage speech. Speak to their level of speech. For for your DS it would've single words mainly, as it was with mine. I started "labelling everything" verbally. Then I would repeat, repeat, repeat and take anything they say and make an assumption of what they said and model it back to them. Do lots of gesturing and pretend you are a CBeebies presenter 
Some examples
Looking at duck pond. DS- uhhh, me yes Duck ( point at duck)
DS holding soft toy bear. I get down on his eye to eye level, so sit on floor or join him at table. Say - bear, ( hide bear) gone, bear gone, peekaboo, hello bear ( hide bear) bear, bear, gone, bear gone. (Can do things like put on his head, make bear sneeze. ) Keep the words really simple, repeat the main word bear a lot.
DS playing with cars, I join in. Say- Fire truck , nee naw, stop. Ohhh fire fire. Fast ( pushing truck quickly) Stop car. Fire truck, nee naw.
Good things are saying likes ready steady, go, in games running or just walking or doing the slide and playing cars. Then you leave the gap, say ready steady.... and hope they add the go !!
Same with nursery rhymes or books. Leave the space (wait ages) and one day the add the words. Twinkle twinkle little ..... the wheels on the ...... ( count to 10 in your head)
When you are out label everything, especially things you see every day. Tree, dog, traffic light, school, door bell (let them ring it.)
Repetitive books they may seem young now for him, but things like dear Zoo, the hungry caterpillar, bear hunt, where's spot. Read everyday and you can also add others he likes.
What is his interests? Can prob suggest some books. Dig dig digging is good.
If it's still on there find toddler club on iplayer there is one on speech. It's 15 minutes mainly for teaching parenting.