How to change the separator "."

Perhaps the question may seem silly.
Can I change the separator between the integer and fractional parts from "." by "," in the entire system? Or, at least in some fields for the export (price, quantity, etc.)

Yes, you can do that editing your currency via the menu System->Currency.

I know that, thanks.
I mean, not for a particular currency, and for the whole system.
This is probably not a good idea?
Or, for example, do this at least for this additional plugin (custom_quantity_weight - www.hikashop.com/en/support/forum/2-gene...w-feature.html#24390 )
That is, the user entering number in the field could use as separator "," (comma).

There is not such option for the whole system.
For that plugin, you could add the code:
$product->ordered_weight=str_replace(',','.',$product->ordered_weight);
at the beginning of both hikashop_product_price_for_quantity_in_cart and hikashop_product_price_for_quantity_in_order functions and that will put a dot for the calculations and probably for the data in the order once created.

Thanks, it worked.
I want to say that I am glad that I found your product. With it I can do my very unusual project.
Special thanks to you, Nicolas, for your patience and quick help.