This is Local Message: https://en.wikibooks.org/wiki/MediaWiki:Addedwatchtext

So It may be possible that It is the sin of Local Message. I think <nowiki>$1</nowiki> in the message is Weird.

@QuiteUnusual was edited that message 8 years ago, so if that user can tell us why this message should not be deleted?

I'm guessing this never worked? (Or, at least, not recently)

	public function onSuccess() {
		$msgKey = $this->getTitle()->isTalkPage() ? 'addedwatchtext-talk' : 'addedwatchtext';
		$this->getOutput()->addWikiMsg( $msgKey, $this->getTitle()->getPrefixedText() );
	}

and

	/**
	 * Add a wikitext-formatted message to the output.
	 * This is equivalent to:
	 *
	 *    $wgOut->addWikiText( wfMessage( ... )->plain() )
	 */
	public function addWikiMsg( /*...*/ ) {
		$args = func_get_args();
		$name = array_shift( $args );
		$this->addWikiMsgArray( $name, $args );
	}

And for plain()

	 * Returns the message text as-is, only parameters are substituted.

@Jayprakash12345: good first task tasks are self-contained, non-controversial issues that require no special permissions and should be well-described with pointers to help the new contributor. Given the current short task description I'm removing the good first task tag. Please re-add the tag once the task description has been polished and provides sufficient information for a new contributor. Thanks!

I think it used to work but even so the message can be deleted and revert to the mediawiki standards.