Broca's Area is the part of the brain believed to be associated with the comprehension of both verbal and non-verbal language. For the purposes of Transcendence, Ehd is a completely fictitious form of human-like primate (we'll call him Homo-savage, m'kay?), who is pretty much exactly like modern humans except he has no Broca's Area in his brain.
What the hell does that mean, Savy? I didn't know this was science class!
What it means is Ehd CAN'T learn to speak. He just doesn't have the ability. He's still highly intelligent and capable of learning many things, he'll just never associate the sounds Beh makes with any objects or actions other than their name-words. He might learn to associate a sound with a desired behavior - that is, he can figure out that if he makes a certain sound (khzz), Beh will put her lips on his and he likes this, but he'll never truly associate the sound with the action like your two-year-old will.
It is very much like your dog, who might learn a whole bunch of commands, but s/he doesn't actually know the word "walk." That doesn't mean they aren't smart - they'll still pick up the leash and carry it to the front door - it just means they don't have the capacity for language.
So, no matter how much Beh tries, Ehd's never going to speak English or French or COBOL. It's just not within his capabilities. He's still a bright boy, though - he'll come around in many ways. At least he's clean now.
If this doesn't make sense, or you happen to be a neurologist and you're mumbling "bullshit" under your breath, just remember while you're muttering that, I'm muttering "artistic license." ;)