code: def _make_unique_slug(slug: str, language: str, is_unique: Callable[[str], bool]) -> str:
          
  
          index = 1
          unique_slug = slug
  
          while not is_unique(unique_slug, language):
              unique_slug = '%s-%d' % (slug, index)
              index += 1
  
          return unique_slug
docs: Guarentees that the specified slug is unique by appending
          a number until it is unique.
  
          Arguments:
              slug:
                  The slug to make unique.
  
              is_unique:
                  Function that can be called to verify
                  whether the generate slug is unique.
  
          Returns:
              A guarenteed unique slug.