Why is the zf2 lucene backlight not working?

Question

Zend Framework

Hello!
Searching with Lucene:

setlocale(LC_ALL, 'ru_RU.UTF-8');
            Lucene\Analysis\Analyzer\Analyzer::setDefault(
                new Lucene\Analysis\Analyzer\Common\Utf8\CaseInsensitive());
            $index = Lucene\Lucene::open($searchIndexLocation);      
            $searchResults = $index->find($validatedQuery['searchQuery']);

Then the words for which the search was performed should be highlighted:

\ZendSearch\Lucene\Search\QueryParser::setDefaultEncoding('UTF-8');
        $doc = Html::loadHTML($high, false, $defaultEncoding = 'UTF-8');
        $doc->highlight($validatedQuery['searchQuery'], $colour = '#66ffff');     
        $highlightedHTML=$doc->getHTMLBody();

Everything works fine with English text, but Russian words are either not highlighted at all, or individual letters are highlighted in other words that do not match the request. Moreover, if the request begins with a capital Russian letter, then the search does not work at all. What can be wrong? Thank you.