TemplateData is a way to store information about template parameters (the description of those and of the whole template) for both humans and machines. It is used by VisualEditor and possibly other tools like Upload Wizard.
Existing template documentation
At Wikimedia Commons, it is recommended to use {{TemplateBox}} with either useTemplateData=1 or useTemplateData=only on the /doc subpage and transcluding it with {{Documentation}} into the template. <nowiki>-tags can be wrapped around the arguments, if required, to avoid templates being expanded.
Newly created template documentation and imports
Another option, especially for imported templates, or for users with JSON experience, is placing raw <templatedata>-tags into the Wikitext of the template, as described in various Wikipediae.
{{References missing}} – generally for files where the description or depiction needs references
{{Datasource missing}} – for own diagrams and maps visualizing data that needs references
{{No source since}} – deletion warning for missing essential source information
{{Sourcefield}} - produces a warning that a file appears to have an invalid entry in its "Source" parameter; for use on user talk pages, not file pages; less serious than the {{No source since}} warning; does not threaten deletion
To add your language to the list of languages supported by this template, please edit the template and add a row to the "{{LangSwitch|}}" construct. It takes the form "|xx= Your translation " (xx being the code of your language)
