The steps to reproduce are unclear to me. Also see https://www.mediawiki.org/wiki/How_to_report_a_bug

If I can paraphrase Juan's bug report, ..

In the transclusion dialog, template 'add parameter' screen, for a template without templatedata (such as cs:wp template commonscat),...

Dont say 'Unknown parameter'.

If there is no templatedata, VE doesnt know about any parameters, so it should not offer warnings that are essentially bogus when it is given a parameter name. The user cant use this 'Unknown parameter' information, so it is scary. Further to that, VE _does_ know that numeric parameters names (like '1', '2', etc) are valid parameter name, so warning 'Unknown parameter' is false in that case.

Juan, if you want to add templatedata to that template, see https://en.wikipedia.org/wiki/Wikipedia:VisualEditor/TemplateData and
https://en.wikipedia.org/w/index.php?title=Template:Commons_category/doc&action=edit

The VE UI for templates without templatedata needs a usability overhaul. Some simple suggestions to improve usability while keeping the current UI structure:

1. say 'This template does not have VE compatible parameter data', and link to the relevant template:blah page
2. dont say 'No unused parameters' because that message is also misleading
3. Instead of 'Unknown parameter' for '1', say 'parameter number 1' or 'first parameter'
4. pre-populate the template form with a parameter '1', place the user in the parameter value field, but allow the user to rename the parameter name in the left hand list.

A more difficult suggestion is to rethink the way the numbered parameter UI works. Putting numbers in a UI, without any explanation, is not intuitive or discoverable. How does a newbie know to enter '1'? The template documentation pages usually say to put in {{foo|blah}} ; they dont say {{foo|1=blah}} so the typical user doesnt know about '1'.

Merging with bug 50735.

• This bug has been marked as a duplicate of bug 50735 ***