Hi,
Okay, I see your problem.
Well, you will have to override some HikaShop views in order to display the price twice.
Like the view "checkout | cart" in order to display the price a second time in the old currency.
Where you see code like that
echo $this->currencyHelper->format($shipping_price, $this->full_total->prices[0]->price_currency_id);
it means that the price is displayed.
You can add some code
echo ' (' . $this->currencyHelper->format( $this->currencyHelper->convertUniquePrice($shipping_price, $this->full_total->prices[0]->price_currency_id, $latis_currency_id), $latis_currency_id) . ')';
to convert and display the price in the other currency.
You have to set the variable "$latis_currency_id" with the ID of your Latis currency (or hard code it).
There are several call of this function (one for each line in the checkout cart) and several views depending what features you are using.
So you might need to override the "cart | showcart", the "order | show" too.
Regards,