Lots of deprecated code in here.
Should be something along the lines of
Linker::link( SpecialPageFactory::getTitleFor( 'CheckUser' ), $this->msg( 'checkuser-log-return' ) );
Sees like it is SpecialPage::getTitleFor, improved in r112586.
Is there any way to improve
$wgOut->addWikiText( wfMsg( 'checkuser-summary' ) . "\n\n[[" . $this->getCheckUserLogTitle()->getPrefixedText() .
ugliness using Linker class?
Can you provide full context? Why do you want to use linker there?
It's in CheckUser_body.php, line 108. I guess there must be a nice way to produce this link.