def __call__(self, old, new):
if not new or not self.precondition():<EOL><INDENT>return<EOL><DEDENT>self.validate(old, new)<EOL>
Validate the `new` translation against the `old` one.

        No checks are needed for deleted translations

        Args:
            old: The old translation.
            new: The new translation.
        Raises:
            A ValidationError with an appropriate message.