OK I managed it myself with an ugly solution which wouldn't work for the main language version where there is no langauge slug if you moved to other country code top-level domain as .lv But for the current situation I can live with that.
Here is the code:
add_filter('pll_the_languages', 'bk_ln_slugs', 10);
function bk_ln_slugs($output) {
$output = str_replace('.lv/menu-categories','.lv/menu-kategorijas', $output);
$output = str_replace('.lv/меню-категории','.lv/menu-kategorijas', $output);
$output = str_replace('en/меню-категории','en/menu-categories', $output);
$output = str_replace('en/menu-kategorijas','en/menu-categories', $output);
$output = str_replace('ru/menu-categories','ru/меню-категории', $output);
$output = str_replace('ru/menu-kategorijas','ru/меню-категории', $output);
return $output;
}