What might their language sound like? Would they have any speech impediments to contend with speaking a Common language?
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Since crustaceans don't pass air through their mouths, the most you could expect sound wise from the mouth would be clicking, grinding, and rasping (like crickets). To form vowels you need a shapeable resonant cavity with a shapeable opening and a source of vibration to modulate. Crustaceans are simply not equipped that way.