I read many many answers. Many have similar questions, but at the end the solution seems to me to build many websites.
My need: Magento 22.214.171.124 to implement 1 website (eg brand.com) with 1 catalog of few products (products are all the same) with different currencies and different prices per country + transactions in the currency of the country NOT the base currency.
Requirement: brand.com/US in USD, brand.com/UK in GBP, brand.com/FR in EUR, brand.com/CH in CHF etc Of course the different folders /US /UK /FR etc will have different languages.
Requirement: Product1 costs 56 USD in US, 57 CHF in Swiss, 62 EUR in EU, etc Product2 same behaviour, etc
Requirement: transactions in US all in USD, in Europe all in EURO, etc
The currency used in transactions must be the one selected by the customer and not the default global one (eg brand.com/US in USD, brand.com/UK in GBP).
OK to consider Magento 2.xx and extensions (either for Mage 1.9 or 2.xx) OK to create many stores (but don't want to have many catalogues as the products are the same)
PS Customers don't mix the carts with products from different stores, as once changing the store, the cart resets.