A character who was previously The Voiceless now talks much more frequently and is, more or less, given a permanent tone of voice.
This was especially prevalent for aged cartoon characters, many of whom originally didn't have voices and were given them in order to make more diverse plots. The reception to this is often mixed due to They Changed It, Now It Sucks.
Note that some of these characters may have already had speaking roles in comic books based on their works. Since comics are inaudible, their voices there are up to the imagination of the readers.
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Anime and Manga
In the Naruto anime, all of Kakashi's ninja dogs could talk during the Hunt for Uchiha arc, whereas in the manga and all previous scenes in the anime the only who could talk was Pakkun.
Persona 4 is going to be downright weird for people who played the game and are used to the Silent Protagonist who only says "Persona" or the name of the Persona he's summoning.
In Jack to Mame no Ki, an anime adaptation of Jack and the Beanstalk, Jack refused to aid the princess of the Cloud Kingdom who had been hypnotized by an evil witch (the giant's mother), and instead slid down the beanstalk with the giant's treasure. While he and his mother celebrated their newfound wealth, Jack's dog (whom was silent throughout the movie) started singing balefully at the moon. Jack saw this as a sign that he should return to the Cloud Kingdom and rescue the princess.
Gon is voiced by Motoko Kumai in his new anime, and the rest of the animal cast is fully voiced as well. He doesn't say much other than his name and make some cutesy noises, but it's still a sharp contrast to the dialogue and sound effect free manga he originated from.
The scarab from the Jaime Reyes Blue Beetle was The Unintelligible, at least as far as the readers were concerned, speaking with incomprehensible symbols that over time became increasingly reminiscent of the English characters, before changing to legible font in its viewpoint issue. For a period during the transition, the scarab's symbols became a form of Wingdinglish.
It was eventually established in the X-Men books that Lockheed the dragoncan speak English, but he prefers to keep the fact a secret.
The Cassandra Cain version of Batgirl learned to speak over a gradual (albeit less so than in Real Life) period.
In Grant Morrison's Doom Patrol, Larry Trainor's Negative Spirit spoke for the first time in its then-thirty-year history. When questioned, it said: "Perhaps I had nothing to say." That was nothing compared to what happened next...
During John Byrne's run on The Thing, Lockjaw of The Inhumans spoke for the first time when Quicksilver tried to pressure wife Crystal to allow their daughter Luna to be placed in the mutating Terrigin Mists, revealing that he was not always a dog. Later subverted/retconned in Peter David's run on X-Factor, when Quicksilver learned that Karnak threw his voice.
For the entirety of his run in Thunderbolts, Man-Thing said not a word. When the title switched to Dark Avengers, Man-Thing was reborn and gained the ability to speak, to the shock of his teammates.
Cartoon characters who didn't talk originally, but who talk in their comic book adaptations, include:
Completely inverted in the Tintin series. Tintin's dog Snowy converses with him in the earlier adventures (a holdover from the sillier, less realistic Early-Installment Weirdness that came with the original newspaper strip), tones it down after the introduction of Captain Haddock, and then by the end of the series is a fully voiceless dog both in means of communication and in behavior.
In Bean, Mr. Bean was changed from being a combination of The Voiceless and The Unintelligible to speaking freely, and gave a speech before a crowd near the end. The premise of the movie sort of forces it, though, since Bean interacts with several characters who speak directly to him (no one ever really did in the original program). The second sort of upholds the status quo, in that he spends most of the movie in France and has little occasion to speak English.
A few brief scenes in the dubbed version of Godzilla vs. Gigan has Godzilla and Anguirus speaking thanks to an alien plot device.
In the first The Santa Clause movie, Comet the reindeer had the most screen time of Santa's reindeer. He looked like a normal deer and mostly grunted and and snorted. In the sequels he looks goofy and cartoony, and can suddenly talk with the speech patterns of Scooby-Doo.
The title character in The Bellboy played by Jerry Lewis, was silent throughout the film until his last few minutes. When other characters asked if he could speak he eloquently explains of course he can. When they wondered the reason he didn't tell them before, he responds..."you didn't ask me".
This was a running joke in The View Askewniverse with Silent Bob. He almost never talks, going well out of his way not to, except for one or two lines near the end of the movie that triggers some great revelation for all of the characters.
Lampshaded in Clerks II: Jay, Randall, Silent Bob, and Dante are all in a prison cell. Jay turns to Silent Bob, expecting some sage advice.
Jay: C'mon, this is when you're supposed to say something.
It was lampshaded as far back as Chasing Amy, where as Bob is about to speak Jay says something like "Great, he's gonna fuckin' say something. He thinks just cos he never says anything that when he does talk it's supposed to be important or something." And Bob even retorts by pointing out that everything Jay says is worthless bullshit.
Lampshaded in Postcards From the Edge, when Suzanne's stepfather says, "Like war buddies."
The film has other mute characters, including the titular thief and many animals. All of these have been given voices in the Arabian Knight version, constantly making jokes.
Michael Myers was a silent (possibly mute?) killer for over seven Halloween movies. But the director's cut of Rob Zombie's Halloween II (2009) actually has Michael scream "DIE!" before killing Loomis.
Transformers: Dark of the Moon features a Laserbeak who can speak, in contrast to the previous incarnations. All in all, it makes him even creepier than other Laserbeaks.
In the Gone in Sixty Seconds (2000) remake, the character of 'The Sphinx' is mysterious due to his muteness, when he suddenly speaks very philosophically at the end of the film with a British accent (actor Vinnie Jones' natural accent). When one of the others says they thought he was from Long Beach, he merely shrugs.
Aversion: Harpo Marx was purportedly offered a large sum to speak one word (murder) in "At the Circus", but turned it down.
In the same film, Harpo does sneeze — clearly saying "A-chooo." In Monkey Business, we hear four-part harmony coming from the barrels, so we can assume he's singing (baritone).
The Mel Brooks film Silent Movie has one word of dialogue in the whole movie. The word is spoken by Marcel Marceu, a famous mime.
The Queen of Tangled gets exactly one line in the mini-sequel, Tangled Ever After. However, it's in an Imagine Spot by Maximus after he loses the rings.
Transformers: Age of Extinction: KSI's drones are supposed to be unable to speak, so naturally their creator is alarmed when Galvatron responds to something Optimus says. This is because he's Megatron reborn.
The third book in the Oz series establishes via retcon that animals from normal lands can talk as soon as they reach magic land. Several books later, Dorothy (and Baum) finally realizes that Toto can talk. After correctly surmising that he doesn't speak because he never did in Kansas and doesn't see the point of starting now, she demands that he speak. He says "Satisfied?" and runs off. Where this trope comes into play is the eleventh book, where he is constantly chatting up a storm for no reason. After the book ends, he's back to being Silent Bob for the remainder of the series.
In Changes, the heroes are temporarily turned into hounds (something like greyhounds, according to Harry). While in this form, Harry is shocked to discover that his dog Mouse can speak. According to Harry's scary-faerie godmother, Lea, Mouse could always talk, but as a human, Harry didn't know how to listen.
Ron, the dragonslayer's assistant in The Dragonslayers Apprentice, does not talk. At all. He could, if he wanted to, he just doesn't, and has mastered the art of nonverbal communication. So the dragonslayer is shocked one morning when his apprentice tells him that Ron got so drunk at last night's party that he spoke a whole sentence in order to proclaim that he liked the sausages.
In the first book of the Elenium, the child Flute doesn't speak at all, but it's made clear that this is because she chooses not to. In the second book, things become dire enough that she decides she has to speak, and henceforth she hardly shuts up.
In the Second Chronicles of Thomas Covenant, Vain, an ur-Vile, never speaks, and simply acts, until the very end of White Gold Wielder, when Vain tells Findail that becoming the Staff of Law is a part of his purpose.
Legacy of the Dragokin: Mordak gains a voice when he evolves from 'walking armor' to 'evil spirit'. He explains this after Kalak expresses surprise at hearing his voice.
Ky Sahra from The Black Company doesn't actually have any speaking lines in Bleak Seasons, the book she's introduced in. She has only a few in She Is the Darkness, but probably has the most dialogue outside of the narrator in Water Sleeps.
Live Action TV
Up until near the end of Season 1 of Skins, Effy didn't say a word. After this, however, the second season gave her her own episode, where she was quiet but talked a fair bit. Seasons 3 and 4 made her a main character and she wasn't particularly less outspoken then any other character.
In the Series Finale of Newhart, the two Darryls, who have been married to two very talkative women, suddenly yell "QUIET!!" to shut them up, much to everyone's surprise. When asked why the two brothers have never spoken before, Larry quips that "they've never been so PO'd before."
Tiny finally says something in the final episode of series one of Raw.
Blue from Blues Clues went through most of the series' run as The Unintelligible, but in 2004 she got a live-action puppet segment where she could speak perfect English.
Clarabelle the Clown was the silent helper of Buffalo Bob on The Howdy Doody Show for years— until this closing shot on the very last show: 
Dumbo (who normally did not talk at all) actually gained the ability to talk in the short-lived children's puppet show Dumbo's Circus, which aired on Disney Channel during the early 1980's.
In Star Trek: Voyager, despite being an recurring extra for all seven years of the series, including being in the pilot, Lieutenant Ayala never actually spoke until "Basics Part II", the first episode of Series 3. He said "Yeah!"
At the start of the first season of Jesse, one of Jesse's brothers had taken a vow of silence. Part way through the season, he suddenly abandons the vow and starts talking (the producers presumably deciding that they had milked the 'vow of silence' angle for whatever limited comic potential it possessed).
In The Protomen's rock opera, in Act I, Dr. Wily has no spoken lines; when he gives orders, they are described in the third person. This changed in Act II, where he had lines and a Villain Song all to himself.
Garfield always talked, but only through thought bubbles in the comics that only the reader could understand, except when he talked with other animals. In the early 90's TV show, he can be heard, but his mouth never moved. In the DVD movies and the recent The Garfield Show on CN, he can suddenly talk normally, and Jon can understand him!
That may be the case for the movies, but in The Garfield Show it seems to be through Animal Talk.
One strip had Garfield with a regular speech bubble that was drawn by mistake. In later strips, Jon reacted to Garfield as if he could understand him.
Becomes a plot point in one illustrated book based on the comic. All animals are capable of speech, but have a rule against using it. Garfield and the other pets in the town sense a huge natural disaster on the way (something that animals in Real Life sometimes do as well) and Garfield proposes that they temporarily relax the ban so they can warn their owners.
Walter Cephus Austridge in Krazy Kat. Strips vary as to whether he's a fluent and eloquent English-speaker or whether he merely says "Geevim, geevim", requiring translation by other characters (or by the author's captions).
Snoopy was another animal that communicated via thought balloons. One strip from the 60s accidentally gave him a regular word balloon and stem—he laps up a potato chip from the floor and says "Anything that falls on the floor is legally mine."
Gronk the dinosaur from B.C. originally could only say his name (in the form of bellowing), but in later strips he started speaking fluently like the other animals.
Grog also spoke in a strip from January 24, 1977.
Bill Watterson has written that avoiding this is one reason Calvin and Hobbes was never given an animated series. He didn't want to ruin readers' perception of how the characters sounded.
X Pac and Jim Cornette tried really hard to stop the WWF from pulling this trope on Kane, but relented eventually with the compromise Kane would only speak with a voice distorting synthesizer. Nowadays Kane is a little(big?) chatterbox.
The normally silent Gangrel started speaking toward the tail end of his WWF run, then went back to being silent after he left.
Orlando Jordan had never spoken a full sentence on WWE television prior to joining John Bradshaw Layfield's Cabinet on Smackdown.
Similarly, Colin Sell in I'm Sorry I Haven't A Clue spoke up (faintly) during a round of "Just A Minim" much to the teams' amazement and Humph's disapproval.
Colin: Who's starting, Humph?
Humph: You decide. You've taken over the bloody show!
The faintness would continue when he spoke later, because he didn't have a microphone. This becomes a plot point in I'm Sorry I Haven't A Christmas Carol, when Ebenezer Scrumph is too mean to supply his assistant Colin Crotchet with a mike, but he turns out to have one at home.
"Susan the Silent" of Finian's Rainbow gains the ability to speak as the result of a leprechaun's wish. Guess she needs a new nickname.
In the Xenoblade, the first Metal-Faced Mechon Shulk encounters is initially silent, but in their next encounter he's quite a chatterbox.
At first, Jak of Jak and Daxter was a Heroic Mime. Then Jak II: Renegade came about, complete with voice. It's lampshaded repeatedly, even before it's invoked: "Say something! Just this once!" The most amusing moment might be when the duo escapes from prison. The first thing that Jak does is walk up to the first person he sees and yell for answers, prompting Daxter to excuse him, saying, "He's new to this whole 'conversation' thing". His first words? "I'm gonna kill Praxis!"
Fairly common in video game series whose origins predate the Nintendo 64/Playstation/Saturn era, at least in the sense that they go from speaking in text boxes to speaking with actual voices. Notable cases go to Mario and Link, who are both heroic mimes, but who have grunts and (in Mario's case) short phrases as soundbytes in newer games.
There was an event at GoNintendo where one can speak to Mario and Wario live and it's voiced by no other than Charles Martinet. Here is an example.
Their cartoon, CD-i, and live-action versions being more talkative, but their reputation isn't good.
In Super Mario Sunshine, the cutscenes had full voice acting (Mario never spoke a single word) and it wasn't even that bad, but the dialogue was so cheesy that it just became silly. Bowser's more high-pitched, cheerful Sunshine-voice has since been replaced by a very dark, demonic-sounding one that can be heard in Mario & Luigi: Bowser's Inside Story.
For an older example, "Mario Speaks!" was one of the big advertising points of Mario Teaches Typing.
Luigi's, Wario's, and Toad's first lines with sound were in Mario Kart 64.
Rayman. In the first Rayman game, he could not talk (except for a single line in the intro). In Rayman 2: The Great Escape, he used unintelligible grunts in a "Raymanese" language (at least in the PC, N64 and Dreamcast version). He finally got full English dialogue (or in whatever language you choose in the menu, which includes the "Raymanese" option) in the PSX and PS2 versions of Rayman 2: The Great Escape and Rayman 3: Hoodlum Havoc provided by David Gasman (who did Rayman's "Raymanese" speech).
This happens to characters who wind up in Brawl. The Pokémon Trainer (aka Red) even speaks a bit, despite traditionally being a Heroic Mime so much so that even when you fight him in Pokemon Gold and Silver and Pokemon Stadium 2, all he ever says is "..."; all his lines, though, are taken from the "Pokemon entering battle"/"Pokemon leaving battle" dialogue boxes used in the games.
Kirby also started to talk, if only to imitate other characters calling their attacks or saying Hiiii as a taunt. This was toned down in Melee, however.
This is also inverted in the case of Donkey Kong, Diddy Kong, and Bowser, who have vocal speaking in their main games, but reduced to primal grunts in the Smash series.
The Legend of Zelda: Ocarina of Time: Sheik's a borderline example. She has almost unnoticeable vocal sound effects in her source game, maybe used once or twice, but come Melee and she has a large (and loud) array of sound effects.
In regards of Metroid, Samus later has full dialogue (enough for fans to complain) in Metroid: Other M. The trope is averted in Metroid Prime 3, in which all characters speak but Samus remains silent; the dialogues between Samus and the speaking characters use words in a way such that the former doesn't have to respond with words, but rather gestures of "yes" or "no" (at one point during the conversation with Aurora 217 from planet Elysia, the player can respond for Samus with a choice between "yes" and "no", just like in any action-adventure game or RPG).
Golden Sun makes the lead character in each game that you're playing the Silent Protagonist. However, given that the two games (GS and GS: The Lost Age) are connected and form a single story together, that causes the silent protagonist of the first game to become Suddenly Voiced, and the inverse happens to the silent protagonist of the second game (suddenly silenced).
Like the Golden Sun entry above, Persona 2: Innocent Sin and its sequel Persona 2: Eternal Punishment have two different protagonists, each of which takes turns being the silent one in different titles.
In Dragon Quest IV, the main character of each chapter is silenced. When they all meet up in the last chapter, each has something to say. This appears to be the model that Mother 3 followed.
The rule in Mother 3 seems to be that the "main character" of the current chapter isn't allowed to talk on the job. This leads to some jarring moments in later chapters when you encounter former party leaders and find that they not only speak, but have distinct personalities. This is actually one of the more artistic aspects of the game since it forces you to identify a character as yourself before seeing how other people view them. It also fits in well with the ending where it's implied that the "Dragon", who is being "passed Lucas's heart" is actually the Player.
There's a single exception in Chapter 5 of the story — a Pigmask gives Lucas a gift, thinking that he's the Masked Man and given that Lucas is implied to be much more amiable than the person he's disguised as, he seems nervously awkward about him accepting this gift and tells him it's "strictly in a friend sense". Talking to him again has Lucas mimic back, "Strictly in a friend sense!", which is very easy to miss—the intent is for you to think the Pigmask is just repeating himself as most NPCs do. Most players don't notice this unless it's pointed out, but the dialogue box has Lucas's name and his mouth even moves.
In Digital Devil Saga, Serph is a Heroic Mime for the majority of the games, but during a flashback his past self has quite a lot to say, and everything he says establishes how muchof a monster he is. It's actually a subversion however, as it's not the same Serph, but rather the base from which the protagonist is created.
The Social Leader in Ogre Battle doesn't talk... until chapter 10, where he/she suddenly appears and talks to the enemy boss.
Star Fox started out Speaking Lylatian, then got fully voiced in Star Fox 64 and future installments... until Star Fox Command went back to Lylatian, with the twist that you could record your own voice using the DS microphone, which would then be sampled and distorted into the Lylatian 'speech'.
The only character that didn't get voiced in 64 was the Trainer in training mode. That is...until the 3DS remake.
Command & Conquer: Renegade gives common soldiers the chance to speak up other than their default responses to move and attack orders in the RTS, often Enemy Chatter (though friendly soldiers also get to speak a bit).
Every single character except for Little Mac and King Hippo in Punch-Out!! Wii, and with appropriate languages, too.
Interestingly enough, in the NES game, Mac and Hippo could speak. Although their words (like everyone else's) were shown in on-screen text.
For that extremely rare non-controversial example, your challenge is to find a single Monkey Island fan who didn't accept that Dominic Armato was perfect for the role of Guybrush Threepwood within thirty seconds of him opening his mouth at the start of The Curse of Monkey Island.
While we did hear his voice as a younger man in Metal Gear Solid 3, it wasn't until Metal Gear Solid 4 that we got hear the elder Big Boss speak. In fact, his first scene occurs right after The Stinger when the character's voice actor is listed in the credits.
A similar example from earlier in the series, which knowing Kojima is probably a subtle Lampshade Hanging: Metal Gear Solid was the first game in the series with voiced dialogue. As such, Snake is unable to recognize his own best friend by voice until that character essentially tells him "it's me you dumb bastard".
Happens to Serge in Chrono Cross. Justified in that when it happened Lynx had traded bodies with Serge, and it's actually Lynx talking, not Serge. Even so, Serge's party members don't seem to catch on that he's suddenly very talkative...
One of the bonus endings for Chrono Trigger has this happen for Crono. Even Marle and Lucca are surprised.
In Disgaea 4, all of the monster types which formerly just made noises were given the option of having voices in the form of short combat phrases like "Here I go!" and "Hiyah!" (Being Player Mooks, they don't get any big voice parts). They had unvoiced dialogue prior to that.
The Legend of Zelda: Four Swords Adventures: Navi Trackers mode had Link as the silent protagonist again, but Tetra, Red Lion and that girl who holds the blue jar above her head, were fluently speaking Japanese, cheering on Link and giving him hints to help him collect 100 hidden coins in the map. Voice acting was however, in this case, integral to the gameplay, as players didn't have time to look away from the GBA screen to look at the TV to read instructions.
Sparx the dragonfly from Spyro the Dragon got this treatment in two stages. First in Spyro: Year of the Dragon, where he gained a kazoo-like voice during the flight levels, and then in A Hero's Tail, when he gained a normal voice.
And the third stage, where he's suddenly David Spade.
Fourth stage, Billy West, for the fifth stage, Wayne Brady.
Spyro: Sparx! It's good to see you too! You okay? Sparx: Huh, you know, little stiff, voice keeps changing, but I'm good.
The Sonic series started with character voices in Sonic Adventure. Before that there wasn't any dialogue in the games at all. It... didn't really help the Broken Base, which started with that game anyway.
Tekken: aside from a few kiais and grunts, all of the characters before Tekken 4 were not very talkative (it was especially jarring in their ending sequences). Julia Chang from Tekken 3 was the first to break the silence in her not-quite standard ending. After that, everybody got into the act in Tekken 4 and every succeeding game afterwards.
Yoshimitsu could also count from the Tekken games, as in Tekken 3 he is heard to recite "Shikisokuzeku" in one of his winposes - part of the Heart Sutra.
Final Fantasy IV DS had some 3D cutscenes with voices. However, this was not cost-free: The previous remake's option to switch party members had to be cut, and with it, the two Bonus Dungeons made for the extended cast.
Final Fantasy characters were voiceless in general (if you don't count the synthesized ones in FFVI) until the tenth installment of the series. Sequels and spinoffs have added voices for many of the other games— the entire main cast of FFVII in Advent Children; 'Leon' and Seifer (among others) in Kingdom Hearts,; the already-mentioned FFIV remake; and most recently, Dissidia gave voices to the heroes and villains of the first ten games.
Torque, the main character of The Suffering never spoke in the first game (aside from yelling and grunting), but was given a deep voice in the sequel, The Suffering: Ties That Bind. Even then he seldom spoke and usually only spoke when the camera was in first person view.
Although the Persona series protagonists make battle grunts and incantations they are otherwise Silent Protagonists, except in the audio dramas where they suddenly engage in conversation. The Persona 3 hero is still pretty quiet and only speaks when spoken to, but the Persona 4 hero is downright chatty, making sure his younger cousin eats well, inspiring his buddy Yousuke and so forth. He only gets chattier in Persona 4 Arena, along with gaining a canon name.
Dead Space. Protagonist Isaac Clarke was a Heroic Mime in the first game. Come Dead Space 2, and Isaac suddenly has a voice. It's probably for the better, seeing as how Isaac's got quite a lot of backstory for someone who didn't talk.
Michael Becket, the protaginst of F.E.A.R. 2: Project Origin, spent the whole game without saying a word, even right at the end where he's raped by series antagonist Alma Wade, but shows up in the sequel F.E.A.R. 3 with a voice and rather angry personality. Understandable, given what Becket's recently gone through.
"Soap" MacTavish from Call of Duty 4: Modern Warfare follows the tradition of being a Heroic Mime. In Modern Warfare 2, he, along with newcomer Pvt. Allen, can speak, but only when the player is not controlling them.
The following Call of Duty: Black Ops has a flashback mission set months after the "official" end of World War II. Dmitri Petrenko, the Russian protagonist of World at War, appears in it and is now voiced.
Sam: Netricsa? Nettie??? You can talk! Netrisca: Yes, it's a bit complicated... let's just say it has something to do with having a bigger game budget. Sam: What game budget?
Pokémon Mystery Dungeon: The protagonist is a standard Heroic Mime, with the twist that s/he does internal monologues relating to the situation at hand. The protagonist finally does speak out loud at the ending of both games, but goes to being quiet and thoughtful afterwards.
Unlike the previous installments, which only have the player say one or two lines, usually at the end of the game, Gates to Infinity has the player speak regularly during plot important scenes, but most of the time he/she will do internal monologues rather than vocally speaking.
A non-serial case occurred in Bastion. The entire game is fully narrated by the character Rucks - even when you talk to other characters, it's just Rucks narrating what you talked about. However, right at the end, just before you're asked to choose your ending, the potential Love Interest, Zia, suddenly gains a voice when you talk to her. The effect is both shocking and striking... and may serve to push you towards a particular ending.
Metal Sonic gains a voice in Sonic Heroes, but goes back to being speechless in every appearance afterwards.
The protagonist in the first Saints Row would only have a male one liner at the end of each campaign. S\he more than makes up for this in the sequel, with not one but six different voices to choose from, and unique dialogue for each. The third game even adds in a female Russian accent and Zombie grunts, and the fourth has the Nolan North voice-set (which is exactly what it sounds like).
Finally, after all 7 of these years, the characters finally get voices in LEGO Batman 2: DC Super Heroes!
At the end of the second Dragon's Lair game, Dirk, having previously only grunted, screamed, and laughed but never actually uttered a spoken word, finally gets to speak when reunited with his wife: "D-Daphne?! YAHOO!"
The title character in the Crash Bandicoot series always did have a voice, but he never says a word mostly since his brain is all wonky. But in the ending of Crash Of The Titans...
Coco: "Let's go home, and eat pancakes!"
In the intro of the original game, he said "Uh-Oh!" (though it's questionable if that counts as a "word").
Yuu Kajima from the Gundam video game Blue Destiny originally went voiceless to reinforce his status as a stand-in for the player (hence his name, a homophone for "You"); this even extended to his appearances in early SD Gundam G Generation games, where his "dialog" consisted of nothing but elipses. When he started turning up as a guest character in later video games like Encounters in Space, Yuu was given a voice (in fact, he's had two: Koichi Yamadera and Junichi Suwabe).
The protagonist in the Saints Row franchise started off mostly mute (having only three lines in the original game) and developed more of a personality as the games progressed. Lampshaded in Saint's Row IV, where the protagonist reveals that s/he didn't say much back then due to nervousness.
In Symphonic Rain, the first three routes have Chris as the protagonist, and unvoiced. After completing them, you unlock a route in which Torta is the protagonist, and thus suddenly loses her voicing while Chris suddenly becomes voiced.
In Another Timeline of Virtue's Last Reward, the player character is suddenly voiced by Troy Baker (Sigma's VA in the promotional anime). This is the first sign that the player is no longer playing as Sigma. The player character is actually an unknown consciousness in the body of K, Sigma's son/clone.
In the Ace Attorney series, only a handful of characters have voices, which in turn only utter brief phrases ("Objection!", "Hold it!", etc.). But the crossover Professor Layton VS Ace Attorney features fully-animated, fully-voiced cutscenes with Phoenix and the usually silent Maya.
Kevin & Kell has been going strong since September 1995, but it wasn't until recently that the two of them were given voices. In a short cartoon from an animation class that Bill Holbrook, the creator, took, Kevin is voiced by Bill and Kell is voiced by his wife Teri.
In Girl Genius, Punch/Adam Clay, a mute construct made by Agatha's birth father and uncle that acted as Agatha's surrogate father for the latter part of her childhood, suddenly has a voice after Gil reconstructed him and Judy after they were torn apart by Von Pinn. In Heterodyne Shows (plays about the adventures of Agatha's legendary father and uncle and their companions), Punch was always portrayed as the Dumb Muscle, despite in real life being quite intelligent (and eloquent once he finally gains speech).
In the 2nd dream sequence there is an voice acted segment where the POV character and the knife wielding woman from the prologue speak, marking the first use of voice acting in the comic.
As of Chapter 4 an entity named Hizrim begins speaking with Asia. Every single one of his lines is voice acted, albeit a little strangely.
The Poopsmith from Homestar Runner has taken a vow of silence, and rarely speaks. The only time he actually said something was in "email thunder", in which he sings. And sounds exactly like one of the Johns of They Might Be Giants fame...
He also says "hello" in the email "different town", as part of Strong Bad's fantasy about things he wishes were different. Once again, TMBG was involved.
Though this applies more to Germaine, who never said a word for the first couple of episodes.
At first, Lopez in Red vs. Blue was just a voiceless mechanic character. Towards the end of the first season, Sarge revealed that Lopez was a robot and that he had ordered a voice chip that would allow full speech. Sarge decided not to ground himself before installing it and static electricity broke the chip. For the rest of the series, Lopez could speak, but only in poorly translated Spanish (Except for one PSA where he spoke French).
The Meta speaks entirely in low growls and snarls. In the prequel sections of Season 9, he speaks on extremely rare occasions... and promptly gets shot in the throat, leading to his later speechless behavior. This makes it a bit of an Inversion.
For the longest time Barry, the editor and all around ace of an assistant for Game Grumps and Steam Train, barring a few instances outside of the shows and one minor line of dialogue for the sake of a joke ("Jon..?"), never communicated in any way other than his standard yellow text. Then came Steam Rolled, Steam Train's equivalent to Game Grumps VS and even there he only spoke using in game communications...at least until the end of the CS: GO episode where he spoke once and has been speaking on Steam Rolled ever since.
The much reviled Tom and Jerry: The Movie aped several Disney-like elements, including giving the titular characters full voices and lampshading it. The second one removed this aspect.
Tom and Jerry were Suddenly Voiced pretty often in their original shorts too, but not often enough for the producers to cast consistent voice actors for them.
Interestingly, Itchy & Scratchy don't have voices in early Simpsons episodes, but were probably later given them to allow for more references to animation.
Several non-canon episodes have used this trope with Maggie, including a few Halloween specials that give her a deep, masculine voice. She actually does speak on the show on two occasions, though: the episode about Lisa's birth and a much-more-recent episode where she says "Ja" in imitation of Springfield's recent migrant workers.
She also said "Daddily-doodily" in the episode where Ned Flanders temporarily adopted the Simpson kids. But her first "official" word, at the end of an episode featuring flashbacks to the horrors of Bart and/or Lisa as toddlers, stated after a Crowning Moment of Heartwarming between her and Homer: "Daddy."
The Pink Panther cartoon gave its cat a debonair British accent, courtesy of Rich Little in "Pink Ice" and Paul Frees in "Sink Pink" ("Why can't man be more like animals?"), for only two episodes. He became The Voiceless, then got a new voice in his 90s TV series, this time by Matt Frewer.
Wile E. Coyote is a notable exception to the rule: he was given a intellectual New England accent for four or five cartoons, and it wasn't made so-much permanent as a running joke (also referenced in Tiny Toons), so fans weren't too incensed . Most of the time, he uses Talking with Signs if he has to make a point. Presumably this is because the Roadrunner is a non-speaking foe, but Bugs isn't.
Curiously, the episode "Hare-Breadth Hurry" had Bugs against a silent Wile E. Coyote. On the other hand, Bugs was explicitly replacing the Road-Runner in that episode.
Both Team Pets, Appa and Momo, spoke during a dream Aang had during the episode "Nightmares and Daydreams".
As per the gimmick of the crossover between Rugrats and The Wild Thornberrys, Rugrats Go Wild gives Spike a voice courtesy of Bruce Willis due to Eliza Thornberry's ability to talk to animals.
Disney experimented with giving Pluto a voice in one of his early black and white short appearances. It didn't work out and he's remained a voiceless character ever since.
Courage the Cowardly Dog went all over the place on this trope. He pantomimes to his owners, but in later seasons talks to outsiders and the audience on occasion.
In his pilot episode, he was voiceless throughout most of the cartoon, but at the very end, he looked directly at the 'camera', and said, "This should not be happening to a dog." Indeed, everyone was voiceless, even Muriel and Eustace, while in the series proper dialogue was always a big part, whether or not Courage was a part of it.
In general though, this trope was inverted. Courage had a lot more to say in the earlier seasons (including a catchphrase), but eventually ended up pantomiming everything (with a few exceptions).
The Great Fairy Rescue shows this to just be Translation Convention, though; scenes from the point of view of human characters show her and the others "speaking" in tinkling noises, as in the original movie.
The first season of Tractor Tom had all the vehicle characters mute and communicated in engine noises, in the same manner of how Lassie communicated with humans. They gained voices by the second season.
Justin in Total Drama Island only spoke one line in the first episode of the first season and was eventually voted off after having said and done absolutely nothing at all since then. When the second season began, he started talking as much as the other characters, with absolutely no questions asked as to why he's so vocal now.
In the Sootyanimated cartoon, Sweep and Scampy went from making squeaky noises (as they did when they were puppets) to being able to talk. Sooty also gained a gimmick: sound effects as per every move of his neck.
Averted on Phineas and Ferb with Perry—-even when the title characters create a special animal translator just to talk to him he goes the entire episode without making more than his usual chattering noise, despite the boys having a conversation with every other animal in town. The closest he ever comes to real speech is one episode where his animal noises are clearly meant to sarcastically imitate Candace yelling at him.
In the above episode with the translator, they actually did use the translator on Perry, but it just repeats the same thing back. Evidently, it doesn't mean anything.
Later parodied; while posing as a human, Perry is forced into a situation where he needs to speak, and then suddenly does in a refined, cultured accent. Then it's revealed he's just mouthing the words to a recording hidden behind his back. Another episode has someone suggesting he can talk treated like an idiot.
A slightly different idea around the same concept: the Teen Titans characters Mas y Menos are regular chatterboxes, but only speak Spanish. An episode near the end of the series features them speaking English when supervillain Control Freak changes the setting on his superpowered remote.
When Cinderblock spoke, it made the villains suspicious. As Jericho speaks with the voice of the victim, that means Cinderblock has the ability to talk.
The fourth movie, Journey Through the Mists, play is straight: when Ducky is thrown into peril towards the end and causes a Say My Name moment amongst her friends, Spike goes, "Duuuhh... duuuhh... duuuhh... DUCKY!!!" Lampshaded immediately after with everybody else doing a collective gasp directed at him.
The carnivorous dinosaurs in the movie series always grunted and roared whereas the herbivorous ones had full speech (except Spike)—until Chomper's re-introduction. In the second movie, Chomper made animal noises just like any of the other tyrannosauruses; but when he was brought back in later movies, he could talk and converse with the main characters. He remains the exception to the rule though. It turns out that said grunting and roaring is simply a different language: By hanging out with Littlefoot and his crew for some time and with his parents the rest of the time, he became bilingual. At one point, they changed them to speaking Spanish for some reason.
An episode of Jimmy Two-Shoes had Jasmine, a seemingly ordinary dog who suddenly spoke the last line of that episode.
Blue in later episodes of Blues Clues and the spin-off Blue's Room. Fans broke into hives.
Inverted with Furrball on Tiny Toon Adventures. In one early episode ("Duck Trek"), he was voiced by Rob Paulsen, but was later replaced by Frank Welker. For some of the first-recorded episodes (including "Buster and the Wolverine"), Welker just gave Furrball an actual voice, but it was later reduced to Furrball either being silent or just meowing.
Also, this show actually marked the first time we ever get to hear Peter Pan sing. Guess who's the only character from the main cast of his debut film that didn't sing at all!
Everyone in Thomas the Tank Engine were all originally voiced by the same actor as the narrator back when the show was still done using models, but eventually got their own voices when the show was starting to be animated using CGI, starting with "Hero of the Rails." In the Japanese version, they were always voiced by individual voice actors, even when they were all filmed using models.
Sassaflash finally got a voiced role while playing Admiral Fairy Flight in "Testing, Testing , 1-2-3" after nearly four seasons of silence. Ditto the two unnamed background ponies portraying Purple Dart and Easy Glider, the former being the first time Tara Strong has had a credited role other than Twilight.
Zig-zagged with Big Macintosh; in "Applebuck Season" he has several full lines of dialogue, but most other appearances have him only saying "Eeyup" and "Nope." When the love potion in "Hearts and Hooves Day" results in his spouting no end of pet names is jarring because of his customary lack of dialogue. Later episodes return Big Macintosh to his customary two phrases (we do see him singing in a couple of episodes, but never solo or in a context where you could really pick out his voice) and he is often prevented from becoming Suddenly Voiced by other characters (cutting him off to insist they already know exactly how he feels, because they disagree with him, etc).
In The One With the gossip column, we get another OOC Is Serious Business moment with him: when he of all ponies speaks full sentences to read you the riot act for what you pulled, it makes an impact.
The Queen speaks in the Tangled Ever After short, but it was only Maximus' inner thoughts.
Predaking of Transformers Prime is seemingly unable to speak while in dragon mode, this changes when he eventually demonstrates the ability to transform in "Evolution."
The Insecticons do not have any lines other than screams and shrieks until the episode Armada, where they break free of Airachnid's control and speak to profess loyalty to Megatron.
Bumblebee's voicebox is restored by Cybermatter during series final climatic battle and he is finally able to speak with his own voice, rather than beeps, for the series finale.
In the episode Minus One, Soundwave is taken prisoner by the Autobots and, after having spent the entire series not saying a word, he finally uttered his famous "Soundwave superior" line from G1.
Blurr of Transformers Animated does not speak or transform during his first appearance while under a human criminal's control. When he does speak in the season 2 finale, he speaks very, very quickly in a call back to his original G1 incarnation.
Venus, Iris' pet venus flytrap in Ruby Gloom, learns to speak the morning of the episode "Venus of Gloomsville."
Jess was mostly a regular cat in Postman Pat. Then he gained the ability to talk when they spun him off to his own show, Guess With Jess.
Snoopy is generally non-speaking (if not exactly silent; he makes "Bleah!" noises and similar, portrayed by Bill Mendelez) in Peanuts animation, even though we can see his thoughts in the comic strip, but the Animated Adaptation of You're A Good Man, Charlie Brown gives him a voiceover, just like the musical. (His Inner Monologue was played by Robert Tower, with Mendelez continuing to provide his vocalisations.)