Speech Delay in a Toddler & No Local Resources

I am from the US but live in Mexico and have a 23 month old boy. He has hit all of his developmental milestones except for speech. The only words he says are Mama, Dada, and eye-eye.

He has said these for months with no further word advancement. His first word (around 1 year) was banana, which he said clearly. He no longer says that word. Every now and then he will do a "normal" babble, but he typically "speaks" with his mouth closed and the sound coming from his throat.

He shows no interest or desire to imitate speech or say new words. If I do get him to answer a "what is that" type of question, his answer is all in his throat. Recently, he has started watching some youtube videos where babies say the names of colors.

I used this opportunity to encourage him to also say the names of some colored sticks that he has. To my delight, he did try to speak the names, but even though he opened his mouth and moved his mouth, the sound was similar to his throat "speech" and did not even come close to the sounds of the colors.

He surprised me further by trying to imitate me saying banana, and once again, it was a sound like his throat speech. I encouraged him and praised him regardless.

His comprehension, both in English and Spanish is amazing. Every day my husband and I are shocked at what he understands both from listening to our conversations and from requests that we make of him.

So I have been relaxed and assuming that when he was ready, he would speak. But hearing his attempts at saying names of colors has gotten me concerned. We are lacking good resources in our area and I am now anxious to know what is going on with his speech development.

Would like to know if I should remain relaxed and give it time or if I should begin exercises with him and be a bit more proactive. Any suggestions or advice would be appreciated.