Impress has a bracket pair callout - which is called "double bracket". It isn't a double bracket. A double bracket is: [[ or ]] and a bracket pair is: [ ] ... and that's what we have. (Well, sort of; see bug 158076)
Change the label of .uno:SymbolShapes.bracket-pair in officecfg/registry/data/org/openoffice/Office/UI/GenericCommands.xcu. Not sure how const ACCNameTypeTable pACCNameTypeTableArray[] in svx/source/customshapes/EnhancedCustomShapeTypeNames.cxx are related but perhaps we need to align this label too. And since we also have "Double Brace" this should be renamed to "Brace Pair" similarly to the "Double Bracket" => "Bracket Pair".