When you don’t want to create the separate .po file or install the translation plugin for a couple of phrases 🙂

function custom_doc_translations($translated){
	$text = array(
		'Search Results for' => 'Результаты поиска',
		'Category' => 'Категория',
	);
	$translated = str_ireplace(  array_keys($text),  $text,  $translated );
	return $translated;
}

add_filter( 'gettext', 'custom_doc_translations', 99 );