Check if a Title object is associated with the given tag.
    This function does not use fallbacks to retrieve title object.

    :param page: a Page instance
    :param lang: a language code
    :param tag: a Tag instance or a slug string.

    :return: whether the Title instance has the given tag attached (False if no Title or no
             attached TitleTags exists)
    :type: Boolean

def title_has_tag(page, lang, tag):
    """
    Check if a Title object is associated with the given tag.
    This function does not use fallbacks to retrieve title object.

    :param page: a Page instance
    :param lang: a language code
    :param tag: a Tag instance or a slug string.

    :return: whether the Title instance has the given tag attached (False if no Title or no
             attached TitleTags exists)
    :type: Boolean
    """
    from .models import TitleTags
    if hasattr(tag, 'slug'):
        slug = tag.slug
    else:
        slug = tag
    try:
        return page.get_title_obj(
            language=lang, fallback=False
        ).titletags.tags.filter(slug=slug).exists()
    except TitleTags.DoesNotExist:
        return False