Adding the current example code to LocalSettings.php yields errors in Mediawiki 1.35.
Topic on Manual talk:Hooks/SkinAddFooterLinks
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To make it work in LocalSettings.php you have to use $wgHooks:
$wgHooks['SkinAddFooterLinks'][] = function( $skin, $key, &$footerlinks ) {
if ( $key === 'places' ) {
$footerlinks['test1'] = '<A href=#>Test Link 1</a>';
$footerlinks['test2'] = '<A href=#>Test Link 2</a>';
}
};