Add title translation.

        :param title: translated title
        :type title: string

        :param language: language for the original title
        :type language: string (2 characters ISO639-1)

        :param source: source for the given title
        :type source: string

def add_title_translation(self, title, language, source=None):
        """Add title translation.

        :param title: translated title
        :type title: string

        :param language: language for the original title
        :type language: string (2 characters ISO639-1)

        :param source: source for the given title
        :type source: string
        """
        title_translation = self._sourced_dict(
            source,
            title=title,
            language=language,
        )

        self._append_to('title_translations', title_translation)