Buzzy don't think I've done anything tbh, with dd I used to talk to her non stop so thought that was why she spoke early but poor ds has been sorely neglected in comparison! Maybe listening to dd talk?
Don't get me wrong, it's still baby talk eg running some words together (inna-in the, wanna- want the/a), missing out letters, not saying words perfectly but other people can understand him too so it is clear enough iyswim.
Oh and ds is stubborn and only says what he wants to say, if you try to get him to repeat something he just laughs or blanks you!
I think the book works on the same premise as the adult one from reading an excerpt of it in the back of mine (Arcadie might come along and correct me though!). Basically there are 5 love languages (Words of affirmation, receiving gifts, physical touch, quality time and acts of service) and it's all about identifying which of these make your dd feel most loved (NOT what you think is showing her love). So for example your dd might feel loved by you if you tell her how great she is, or, that might mean nothing to her and she needs a cuddle to feel loved. Or she might feel most loved when you do things for her or when you give her small gifts, or just when you send time focusing on doing something with her.
Obviously the book goes into far more detail but once you know which language she speaks then you can do little things everyday that show her that you love her (my dd is maybe a bit young but I think hers is quality time and that is why she played up so much wrt potty training...)