"machinevision-machineaidedtagging-intro": "Review suggested tags of [[c:Commons:Depicts|depicted objects]] in images. Only user-confirmed tags are added to images. For more information, check out the [[c:Commons:Structured_data/Computer-aided_tagging|project page]] and [[c:Commons_talk:Structured_data/Computer-aided_tagging|give feedback]] on how to make this tool more helpful!",
The c interwiki prefix is WMF-specific and doesn't exist by default in the software. Assuming the extension is not expected to be installed on other wikis, I suppose this isn't needed, either.
During development, both the c and the Commons namespace don't exist (the latter is even more specific, to the commons.wikimedia.org wiki).
In general for these kinds of messages we refer to the local Project: namespace by default, which wiki editors then populate with documentation and/or redirect accordingly. In this case Project:Depicts would achieve the same effect and work the same way, given that Project is a language and wiki agnostic alias for the project's meta namespace, which is Commons on commons. That is, [[Project:Foo]] will directly and explictly result in a link to /wiki/Commons:Foo.
Currently, these links become client-side redirects via /wiki/c:Commons:Depicts which also incurs extra network-server roundtrips. They are also red links by default during development that can't be created easily (unlike Project:).
Would recommend changing using Project: for these instead :)