In Peter Jackson's movies there seem to be different kinds of Orcs and I get that. It's the Uruk-hai I'm a little unclear on. In Fellowship of the Ring and The Two Towers, the Uruk-hai who are taking Merry and Pippen to Saruman speak well (as do the Orcs who meet up with the Uruk-hai in Rohan). However, at the Battle at Helm's Deep, I cannot recall a single Uruk-hai uttering a word -- they grunt and growl and roar. And then we move on to the Battle at the Pellenor Fields, and the Uruk-hai are back to talking with full speech again. Regarding The Two Towers, are the Uruk-hai who fight at Helm's Deep just killing machines? Or are they speaking their own language, that we just can't understand and isn't subtitled? Or is it something else? I thought the Uruk-hai were supposed to be "perfected" beings. It seems speech would be part of the package.
Note that it is explicitly stated that the Orcs (and Urukhai) are from different regions and have their own languages/dialects, and the dialog in the books is when they are conversing in common speech. When Pippin and Merry are captives, there are orcs from Mordor, the Misty Mountains in the North, and Isengard at the least.
To Pippin's surprise he found that much of the talk was intelligible; many of the Orcs were using ordinary language. Apparently the members of two or three quite different tribes were present, and they could not understand one another's orc-speech.
They do taunt the Rohirrim at helms deep:
The Orcs yelled and jeered. 'Come down! Come down!' they cried. 'If you wish to speak to us, come down! Bring out your king! We are the fighting Urukhai. We will fetch him from his hole, if he does not come. Bring out your skulking king!
Most of the roaring and snarling is a fabrication of the movies. They were far more likely to swear.
Note also that Uruk = Orc and Urukhai means high orc or big orc, and they were certainly NOT manufactured by Saruman as depicted in the movies. Indeed, one of the bands of in Mordor who deal with Frodo's body are Urukhai.
If you remember, the army that assailed Helm's Deep was a legion of newborn, but battle ready uruks.
They knew no culture but to march, fight, pillage, and roar. They very well may have not knew how to speak. But, as creatures reborn of pure evil, it would make sense that Sauroman and other satanomancers would be able to communicate to them regardless of the language they spoke, because their souls are bound to serve.
So in the book, at the Battle of Helm's Deep, the Orcs don't speak any Common, but they do grunt and make other noises.
In the movies, Jackson expanded on the Uruk'hai by having them talk more and take a bigger part in the story. Generally, I believe the army attacking Helm's Deep was mostly regular Orcs and Hillsmen, not an army of only Uruk'hai.
So, to keep the battle similar to how it appears in the book, Jackson did not insert any dialogue between the two groups.
Additionally, this can probably be explained in-world as there was no reason for dialogue. It wasn't a battle where negotiation was an option.