Hi

Is it possible to make each level of categories in new dropdown (example is in Epsilon theme) in Sigma theme? Is there some simple change?

Yes, there is osclass function for that, check categories frm class... Do not remember bane.

Will check it out, thanks.

Ok, I found this solution.

In "item-post.php" I changed

<?php ItemForm::category_select(null, null, __('Select a category', 'sigma')); ?>
to this

<?php ItemForm::category_multiple_selects(null, null, __('Select a category', 'sigma')); ?>
Dropdowns are working fine, I still need to find out why translation doesn't 

Ok solved, I didn't translate it in core.po 

Correct 

no work, no exist function category_multiple_selects in class category