There is one hook in Special:WhatLinksHere and that cannot be used to implement this feature in the Translate extension. Moving to "cross projects" column because I cannot set the priority.

There is one hook in Special:WhatLinksHere and that cannot be used to implement this feature in the Translate extension. Moving to "cross projects" column because I cannot set the priority.

Thanks for the note. Ultimately it will be good to be able to even select a specific language to be shown but I guess on step at a time is the best approach.

Okay, so, assuming hooks can be used to allow this, there needs to be a way to detect page translations via sql.
Currently, the logic for detecting them to prevent direct editing is:

[...]
$page = TranslatablePage::isTranslationPage( $title );
if ( $page !== false && $page->getMarkedTag() ) {
	[...]
	return false;
}
return true;

public static function isTranslationPage( Title $title ) {
	$handle = new MessageHandle( $title );
	$key = $handle->getKey();
	$code = $handle->getCode();
	if ( $key === '' || $code === '' ) {
		return false;
	}
	$codes = Language::fetchLanguageNames();
	global $wgTranslateDocumentationLanguageCode;
	unset( $codes[$wgTranslateDocumentationLanguageCode] );
	if ( !isset( $codes[$code] ) ) {
		return false;
	}
	$newtitle = self::changeTitleText( $title, $key );
	if ( !$newtitle ) {
		return false;
	}
	$page = self::newFromTitle( $newtitle );
	if ( $page->getMarkedTag() === false ) {
		return false;
	}
	return $page;
}

public function __construct( Title $title ) {
	$this->title = $title;
}

A bad way to try and add sql filtering would be to ensure that the page title doesn't end with a language code, but that would also exclude translations that are not a part of the translate system.

If it need to be done with SQL, perhaps setting a prop in page_props (or revtag) could make it fast and accurate enough?

Implementing this (to reduce that long output list) would help a lot with updating now defunct anchor links pointing to restructured documentation pages (random example), and finding links on mediawiki.org pointing to removed function doc pages in MW Core (random example).