To solve Django-Taggit limitation such as unicode slugify and generic foreignkeys integer problems, I customize and inherit some code as below. It provides unicode slugify based on changing django default slugify into unicode slugify module and string object id for GFK

model_for_taggit.py

from django.db import models
from django.utils.translation import ugettext_lazy as _

from taggit.models import Tag, ItemBase

# it is required to support unicode tags slugify
# https://github.com/mozilla/unicode-slugify
from slugify import slugify as default_slugify


class UserContents(models.Model):

  id = models.CharField("Content ID", max_length=50, primary_key=True, blank=True)
  title = models.CharField("Content Title", max_length=140, default='', null=True, blank=True)
  description = models.TextField("Content Description", max_length=2000, default='', null=True, blank=True)
  # it provides custom TaggedItem by through attribute
  tags = TaggableManager(through=UserContentsTaggedItem)
  datetime_modified = models.DateTimeField(null=False, auto_now=True)
  datetime_created = models.DateTimeField(null=False, blank=True)


class TagExtended(Tag):
    # store created datetime with tag to analyze tagging data
    datetime_created = models.DateTimeField(auto_now_add = True)
    
    # inherit slugify from TagBase
    def slugify(self, tag, i=None):
        slug = default_slugify(tag)
        if i is not None:
            slug += "_%d" % i
        return slug


class UserContentsTaggedItem(ItemBase):
        
    tag = models.ForeignKey('TagExtended', related_name="%(app_label)s_%(class)s_tagged_items")

    # store created datetime with tagged contents to analyze tagging data
    datetime_created = models.DateTimeField(auto_now_add = True)
    
    # it supports string pk of content_object
    object_id = models.CharField(verbose_name=_('Object id'), max_length=100, db_index=True)    
    content_object = models.ForeignKey(UserContents)
    
    @classmethod
    def tags_for(cls, model, instance=None):
        if instance is not None:
            return cls.tag_model().objects.filter(**{
                '%s__content_object' % cls.tag_relname(): instance
            })
        return cls.tag_model().objects.filter(**{
            '%s__content_object__isnull' % cls.tag_relname(): False
        }).distinct()