You need data redundancy... since all data will need to be translated into all of the languages you support.
It will never work that you type in one language and it is properly translated into all that you support.
You can maintain a currency conversion rate in your database to calculate currencies or find a third party service for it.
Subdirectories for each language actually makes a lot of sense for a lot of reasons. Since any translated data would not be redundant. You could always expose or update more than one table or use one database table for content for the admin section so that data is never truly redundant in the user experience or database regardless of front end directory structure.