Sawyer is 18.5 months and, like Margot's Jacob, can understand instructions clearly (though often ignores me anyway!) but doesn't say much at all really.
Something I have found lately though, is that he IS saying words, it's just that we haven't been understanding what he meant because his pronouncition was off iyswim. So recently it suddenly occurred to me that he has been saying Grandma for months, but because he says 'Agma' at the moment, I didn't realise what he was saying.
Suddenly lately he has started babling for England and every so often another 'was that a....' word comes out.
As long as LO understands, that's the main thing and I wouldn't worry x