HTML entities for non-breaking spaces should not be visible in the label, see screenshot:
This bug is similar to T142882.
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Relevant code in FlowPresentationModel.php:
// notification-dynamic-actions-flow-board-unwatch // notification-dynamic-actions-flow-topic-unwatch $link['label'] = $this ->msg( 'notification-dynamic-actions-flow-' . $type . '-unwatch' ) ->params( $stringPageTitle, $title->getFullURL( $query ), $this->getUser()->getName() ) ->parse();