When creating or editing a node, under the body, I get a list of tips for the filters included in the current text format.
For interwiki the tips are:

Easily link to terms in various wikis. For help, see [interwiki].

[interwiki] is a link to /interwiki/text-format-name .
However when users go there (even an admin), they see an Access Denied message.
This also happens for the /interwiki path.