Certainly the classic D&D language minigame is a nice bit of resource managment ("Who speaks sphinx, c'mon someone?"), but for my Lyonesse-inspired OD&D game I went whole hog with "pretty much everyone speaks the same language" and is usually pretty chatty. Foreigners, Dwarves, Goblins, Giants, even Zombies ("Oy! I'm already dead mate, no point in threatenin' me!") and Chimerae.
It ties in with delight in Jack Vance's eloquent monsters ("Please quit struggling and lie down peacably so I can enjoy eating you sir...") and it also comepletely removes the character generation speed bump of languages spoken, which I've been pretty much mashing through and ignoring for years now.
The one phenomenon I've noticed with this is that sometimes a player will continue to attempt negociating with or browbeating a monster after hostilities have commenced ("Stop! Stop!","There's no talking me outta eating your man-flesh, arrgh!"), which is pretty hilarious.
The session before last a PC was transformed into a toad by hag; although a traditional interpretation of such a transformation would involve him being only able to ribbit and croak, I got my head out my ass and ruled that the toaded PC was indeed capable of speech. Unsurprisingly, much hilarity ensued and the player was able to participate in the following events, so it worked out pretty much perfectly. Plus the player attempted talking like a toad, which was a real laff riot as well.
I also quite enjoy having counterintuitively chatty monsters such as zombies and chimerae, which certainly ramps up the absurdity and the fairy tale vibes, although I haven't gone completely off the deep end and had ordinary animals speaking, now that would be just too wacky for this particular game.