17,5 month old not using consonants anymore

Hi! My son will be 18 months old in just a couple of weeks and I'm a bit concerned about potential speech delays. I just wanted to see if other people have experienced this before I take him to a specialist.

So a bit of context:

  • We speak 85% in Greek to him at home and 15% in English, as his dad is bilingual. He's been going to the nursery full time since he turned 1 year old, where they speak to him in English (though they know a couple of Greek words).
  • We read books to him both in Greek and English.
  • He started babbling using consonants before he turned 1. He used to clearly say mamamama and babababa (babas is greek for daddy), but we weren't sure whether he knew what they meant. Probably not, although when he wanted comforting he often cried "maaaaa".
  • At some point he stopped babbling and switched to making vowel sounds that imitated singing and tried to communicate with us with "ah-ah-ah" and things like that. That happened after he turned 1, but not sure how many weeks/months after, so I'm wondering if it concided with him going to the nursery and listening to English all day instead of Greek.
  • He currently understand MANY words and phrases we tell him, in both languages, and is able to communicate by pointing and, when he needs something, shouting. He likes imitating singing using vowels. He can do some animal sounds (not many) but he mostly uses vowels. He often babbles "wawa" (so not exactly vava as the consonant is not clearly heard). When I ask him who I am, he says "wawa", I correct him but he doesn't say mama. Same with his dad.
  • He's ok in other milestones I guess. He walked without assistance when 15,5 months old, which is not very early but still not too late either.

I'm just wondering if it's part of his personality that he takes his time doing things but I might be reading too much into it. It looks like he's not bothered to talk to express his needs as he can point and/or shout/make a vowel noise.

But it's really confusing me that he used to be able to say consonants, even out of context, and now he doesn't. And of course, other than animal sounds and sign language, he hasn't said any real words with context, while he is supposed to say at least 10 at this age apparently. But he does understand everything we say. Anyone can relate?