The Babble Band is a ribbon worn around the tongue that alows someone to speak the same language as the one being spoke to you. But as pointed out by Genny Measly how would you know what they were saying to you? But I suppose you could always just tell them that you don't understand them.
For Barry's birthday in Barry Trotter And The Unnessisary Sequal Ermine got him a babble band which is when Genny pointed out their one problem. Ermine suggested that mebey they came with some earmuffs.