Adding slug convert option

[hwshim0810]

Unidecode translates non-English words, I have added an option to use the original language as a slug.

I tried to add a test, but adding non-English characters to the test code seemed to be a problem.

[codecov-io]

Codecov Report

Merging #572 into master will not change coverage.
The diff coverage is n/a.

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##           master   #572   +/-   ##
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  Coverage      94%    94%           
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  Files           4      4           
  Lines         434    434           
  Branches       77     77           
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  Hits          408    408           
  Misses         16     16           
  Partials       10     10

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[jdufresne]

I tried to add a test, but adding non-English characters to the test code seemed to be a problem.

Can you clarify? It should not be. We should add a test to verify the behavior before merging.

[auvipy]

could you please rebase?

[lucemia]

+1 for this PR.

Without this PR, django-taggit has serious performance issue in any non-English applications.

django-taggit/taggit/models.py

Lines 61 to 71 in 83fe619

	i = 1
	while True:
	slug = self.slugify(self.name, i)
	if slug not in slugs:
	self.slug = slug
	# We purposely ignore concurrency issues here for now.
	# (That is, till we found a nice solution...)
	return super().save(*args, **kwargs)
	i += 1
	else:
	return super().save(*args, **kwargs)

Insert a new non-English tag to existing 10,000 tags, will cost 10,000 query.

[rtpg]

@lucemia thank you for pointing this out, I hadn't quite absorbed this fact when this had come up.

To be honest I don't quite know what the value of "ascii-fying" everything for slugs is, it does feel a bit silly. So I think that having this setting, and having it be the new default (rationale: if you're using characters outside of ascii, it's very likely you find that important for your language).

[rtpg]

Of course after thinking about this a bit more I am reminded that slugification exists primarily for URLs and the like.

For example if you have a URL scheme like /posts/<tag>/ then you want the tag to... at least not contain slashes I suppose.

I am going to try and dig up some ideas here for how to handle this.