I know of at least one computer game, Wizardry Gold (an installation in the D&D inspired Wizardry series) that ''did'' allow the player to input their own dialogue, and the NPCs would respond to it. The game is actually quite old, but the ability of the computer to come up with a reasonable response was actually fairly good. The problems in this case were that it made the game extremely ''difficult'', since it was often hard to [[YouCantGetYeFlask think of something appropriate to say]], and it was even harder to give NPCs distinct personalities with which they could respond.
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Related trope idea: games and possibly old cartoons where all the characters are mimes, and where the story is told entirely through visuals instead of text/dialog. The original ''SonicTheHedgehog'' series, the intro to ''SuperMarioWorld'', ''{{Game/Another World}}'' and ''LegoStarWars'' are all examples. --DocumentN
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{{Bob}} Restored the ZeroPunctuation quote since no justification was given for cutting it.

->''"Ever since the {{Doom}} [[SpaceMarine marine]] first [[BonusLevelOfHell grimaced his way up Satan's arse]], [[FirstPersonShooter First-Person Shooters]] have been defined by the faceless, [[TheVoiceless voiceless]] dorks that [[HealThyself tread on their first-aid kits]]. One could almost say that each era of gaming is defined by its anonymous, taciturn underdogs if one wanted to sound like a twat."''
->-Ben '[[ZeroPunctuation Yahtzee]]' Croshaw

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Does Kirby count? He never talks in his games.

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Okay, this is not a video game which is why I'm checking before adding but ''Gone-Away World'', a novel by Nick Harkaway features an entire troupe of heroic mimes. Literally. If not here, where?