Celegorm will understand Huan in the way that Han understands Chewie without subtitles or Luke understands R2 when they are in the X-wing. Obviously, Huan will have to 'speak' in Season 5, as Beren and Lúthien don't have Celegorm's skill.
I agree that we want talking Ravens. It would be cool if you could just train an actual raven to say the lines
But since a raven's voice is practically indistinguishable from a human's voice, I'm sure voiceover would be fine as well
I don't really have anything against talking animals in a fantasy environment with sentient creatures. The Elves do call themselves 'Quendi,' though - those who speak. We should be careful not to overdo it with the talking animals.
I might have to go re-read Frodo's encounter with Shelob, but what I recall from that does not involve speech. The eyes are intelligent, and full of hatred, so Frodo knows he's up against a thinking foe, not a beast...but...they don't exactly trade words. On the other hand, Gollum has obviously found a way to communicate with Shelob, so while they might not be talking, they are working together. Sam talks to Shelob, too, so he expects to be understood. This is a contrast with the talking spiders of The Hobbit...but also possibly quite intentional on Tolkien's part to move away from that. Just as the conversations with eagles in The Lord of the Rings are all Gandalf-centric and (mostly) off screen.
So, in other words, just because we clearly have talking ravens, thrushes, eagles, and spiders in The Hobbit does not mean we should be in a hurry to populate Beleriand with talking animals. Maybe rather we should be thinking of populating Beleriand with those who can speak to/understand animals.
On the other hand - presumably Tevildo talks while in cat form, and Thorondor talks while in eagle form. Draugluin has dialogue in the published Silmarillion, as does Ungoliant. We certainly can't *avoid* talking animals!
A separate discussion is the external issue. The Execs are not convinced that talking animals would look anything but silly on film, and so are mostly in favor of minimizing that. If we want a character to have a voice, we should probably advocate specifically for that in the episodes where it would be relevant. I doubt they're going to veto Thorondor or Huan having voice actors, but they were very reluctant to let go of Ungoliant talking while in humanoid form only. She does not transform into spider form until after her recruitment talk with Melkor. Of course, we *did* wind up giving her dialogue for her final fight with Melkor in which the balrogs save him and drive her off.
Peter Jackson managed to get through
Lord of the Rings on film without any talking animals. We can't get through the
Silmarillion that way, so we have to make different choices. Those other choices could involve telepathic communication without mouths moving, but there will likely be communication that the audience is aware of and understands. (Not just Saruman getting a message from a flock of birds and delivering that news to the audience.) But...we likely won't be quite using Hobbit-levels of talking animals, either.