About [[MediaWiki:Apihelp-sitematrix-description/en]]

I think that for a start, to have less confusion, we could revert gerrit:212925.

Or we could improve the original sentence like this:

• "The code is either the unique identifier for specials or, for languages, the project code." →
• "The code for information about a site to return is either the unique identifier for specials or, for languages, the project code"

So it should be more clear that it's intended to describe the code in output for for "smsiteprop" parameter and not for "smlangprop" (see w:Special:ApiSandbox#action=sitematrix).

Whether API field(s) should be renamed (phab:T100459) would be a separate issue then.