I'm making this post to clarify a few things about this long-resolved situation. For your information, Wikipedia wouldn't allow a DISPLAYTITLE containing the "|" character even with the
{{!}} workaround, as it enforces a server-side setting called
$wgRestrictDisplayTitle that causes DISPLAYTITLE magic words to only work if the title that they're given resolves to the same canonical pagename as the actual page title. As "|" can't be in a page name, it can't be in a DISPLAYTITLE there either, even if you escape it using the
{{!}} magic word. As a formal encyclopedia, Wikipedia enables that setting to keep with the wiki convention that a page's title is its name, and thus can be used for linking to it; however, Fandom, which is somewhat less formal, has that server setting disabled, meaning that the
{{!}} workaround works on Fandom wikis, as seen
here.