Woo Poly + Payment gateway – reduce stock issue

Hello.
I’d like to ask for help or pointing me in the right direction on how to solve my issue.
So, I am using a plugin for Czech gateway GoPay on my site. This plugin seems to have a little problem with handling synchronization of reducing stock. When I buy an item, the stock is reduced -1 per current language version but always -2 for another language version.
I asked a developer about this and got the response that they don’t provide support for Polylang nor WooPoly. The only information I got is that the reduce stock level is handled by this piece of code.

$stock_reduced = get_post_meta( $order_id, ‘gopay_reduced_stock’, true );
if( empty( $stock_reduced ) ){
wc_reduce_stock_levels( $order );
update_post_meta( $order_id, ‘gopay_reduced_stock’, ‘reduced’ );
}

Could you please know what the problem could be here?
Thanks.