There is too much burden attached to working with KeyEvenTranslations.tr
so I rarely use it.
You can try an alternative: DevTools`:NotebookActions
:
ResourceFunction["GitHubInstall"]["kubapod", "devtools"]
Needs @ "DevTools`";
NotebookActionsEnable[];
EditNotebookActions[];
add a cell with:
<| "Label" -> "ClearCell"
, "ShortKey" -> "c"
, "Action" :> FrontEndExecute[{
SelectionMove[InputNotebook[],All,CellContents]
, NotebookDelete @ InputNotebook[]
}]
|>
Press Save and Test.
And you are ready to go: Ctrl+, and then c should clear cell contents.