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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def active_language(self):
 """ Returns active language. """

        # Current instance language (if user uses activate_language() method)
        if self._language is not None:
            return self._language

        # Current site language (translation.get_language())
        current = utils.get_language()
        if current in self.supported_languages:
            return current

        # Default language descriptor
        return self.default_language