Thank you for help, but it's all a little complicated... in my case I must to create 3 custom fields + language constants + change the code which does not gives flexible description. Tell me what you think about my decision - I created one custom field which has text type and added the code in show_block_custom_main.php:
$array = array(
'STRAWBERRY' => '<a href="strawberry.jpg">strawberry</a>',
'ANANAS' => '<a href="ananas.jpg">ananas</a>',
'APPLE' => '<a href="apple.jpg">apple</a>');
$description = str_replace(array_keys($array), $array, $this->fieldsClass->show($oneExtraField,$value));
echo $description;