Both my kids are bi-lingual- French and English.
They are fluent in both.
My son, however, has a delay in speaking. NOT anything developmentally 'wrong' with him (he was fully assessed), but boys are just generally 'slower' in talking than girls.
Our Speech Therapist says that 80% of her clients are "boys" and they are just slower in talking. It is the gender differences in normal development.
For me, since there is a 'free' service in my area, I do have speech therapy for my son. He is now 2.5 years old, and has progressed in 'english' speaking very well... but also in tandem with his age.
I would not worry about it... unless the Pediatrician says so. Or, you can get him assessed. Ask your Pediatrician for your Regional Center that does these 'free' services for children... the 'zero-to-three' program.
Again, your son is only 20 months old. My son, started his speech Therapy at about that age. Again, I do it because it is free, and it gives me & my son tips on how to 'encourage' speaking. And he enjoys it very much. Our Therapist is great.
My son, also knew sign language, and both languages. AFter being assessed, he was even found to be advanced in some areas, developmentally. And he is very smart and understands very complex things we tell him. So, there is nothing 'wrong' with a child for speaking at a slower pace... BUT, you can get an assessment to rule out actual real 'problems.' Which my son does NOT have.
The thing is, I do NOT think of my son as having a "problem" or him being "delayed or slower" than other kids. He is just bi-lingual, and this also plays a part in the whole scheme of things. BUT, there is nothing 'wrong' with that.
A child will talk when they are ready. My son is the same way. But, his progress is just not like my daughter, who was VERY talkative. My son, also can say French words too. Both my children do.
You cannot 'force' a child to speak... but you can use techniques or encourage them. Each child is different.
I don't think there is anything 'wrong' with your son. Remember, he is also bi-lingual. So even if he is not speaking at the level you want... he is absorbing everything and getting it.
I am glad though, that I have the speech therapy for my son, I believe it has jump started his enjoyment to talk. He was previously a little 'shy' to say things.
My husband only speaks to my kids in French. I only speak to them in English. That is the best way to teach bi-lingual kids. Their 'speaking' will blossom in time....
Kids who are bi-lingual have DOUBLE the amount of things they must learn... and even their brain synapses and connections are more developed because of it. Their understanding of speech in conjunction with the coordination of their mouth/sounds will come in time.
Remember, even if he just babbles and makes sounds, THIS is "talking." Talking does NOT have to be PERFECTLY articulated words as adults know it. Talking for a child this age does NOT have to be 'real' words, as you said. Your sone IS talking, and making sounds... all of this IS talking and precursors of talking. Articulation of words is a progression. A 2 year old will not 'talk' like a 5 year old.
It all has to be age appropriate.
Einstein did not talk until 3 years old. Mozart was also 'slow' in talking. No biggie. Unless there is something biologically/developmentally 'wrong' with your child... I would not worry. But things like Speech Therapy can be helpful.
*Side-note: I would not expect him to 'talk' by his 2 year old birthday. He already IS talking, after all. And, if you are concerned about what others say, just ignore it. There were 2 times when a Mom commented on my son 'not talking yet..." and it was irritating and she then thought my son was "dumber" than other kids because he was not 'talking' like she highly thought he should. So what. My son IS smart and advanced in many areas, he is just not ready to talk at full-speed like other kids. No biggie. My Speech Therapist says my son is very bright in comparison and is talking at a good progression for HIS pace.
All the best,
Susan