roxy, dave, and karkat all speak carapacian (though dave and karkat less fluently) and they like to use it to annoy people who don’t
roxy has a carapacian accent with it (probably) being her first language, which mostly means she mumbles a lot (since that’s how carapacian language is described in canon)
dirk had a mishmash of accents from various childhood learning videos and kids tv shows alpha dave left but he seems the type to go like “Oh fuck my voice sounds kind of weird? Time to fixate on that and practice and train until i can pronounce it perfectly.”