Topic on Help talk:TemplateData

All TemplateData would include a link to Wikidata.

Why?

Because can be used in other projects.

Agree.

Without retyping all the data, fields an information.

I don't think I understand your suggestion. This is the TemplateData for the English Wikipedia's "citation needed" template:

<templatedata>
 {
 "description": "The template is used to identify claims in articles, particularly if questionable, that need a citation to a reliable source.",
 "params": {
 "date": {
 "label": "Month and year",
 "description": "Provides the month and year of the citation request; e.g., 'January 2013', but not 'jan13'",
 "type": "string",
 "autovalue": "{{subst:CURRENTMONTHNAME}} {{subst:CURRENTYEAR}}",
 "suggested": true
 },
 "reason": {
 "label": "Reason for citation",
 "description": "A reason as to why, or for what content, the citation is needed; use single quotes, if any",
 "type": "string"
   }
  }
 }
 </templatedata>

No editor or reader at any article ever sees that. I don't think it makes any sense to add a Wikidata link to the TemplateData.

Are you looking for a sort of magic infobox, so that you can type {{infobox}} and Wikidata fills in all the fields for you? That already exists, and it has nothing to do with TemplateData. Have a look at w:es:Jimmy Wales for an example of a long infobox that is mostly pulled from Wikidata.

From your example : "description": "The template is used to identify claims in articles, particularly if questionable, that need a citation to

It would be translated to other language, I e. Spanish:

"description": "La plantilla se usa para identificar afirmaciones en artículos (and so on...)

So, this translation into Spanis of the template can be used in Wiktionary in Spanish, Wikipedia in Spanish, Wikibooks in Spanish... Translate once, use in several places.

On the other hand, this is seen in a forms way, when editing TemplateData.

TemplateData editor method

This is the simpler way to add or edit TemplateData, possible for inexperienced users. </translate>

The TemplateData editor is a graphical user interface for adding and editing TemplateData. It is part of the TemplateData extension. It is accessible by going to any template's page (or documentation subpage) and clicking "Edit" or "Edit source".

After clicking "Edit" or "Edit source", you will see a button above the editing area and page title that says "Manage TemplateData".

Clicking this button will enter the TemplateData editor. If the page you are on already contains TemplateData, this will automatically show here.

Because we don't have Global templates, it's unlikely that anything would get re-used in multiple places.

We can use TemplateData in Wikidata for templates in all sister projects and so, the template documentation can be reused in multiple sister projects. Translate once, reuse several times. Also could be used the Wikifunctions wiki.