The validate function does exactly what it sounds like it will do. It validates the command in any way that you provide in the validate function. You can return either a string, as shown above, to use in your "onError" property, or return a boolean/undefined to default to a generic error code of "INVALID_ARGUMENT". Whatever string is returned from the validate function is passed into the "onError" function as the parameter "error".
language: keyof import("cdcommands/src/Base/Handling/Languages.json")