Authorize.net itself boosts it supports multiple currencies: https://community.developer.authorize.net/t5/The-Authorize-Net-Developer-Blog/Authorize-Net-Expansion-into-Canada-the-United-Kingdom-and/ba-p/33690
The list of payment processors shows a 'blank' when it comes to regional support for the Authorize.net payment processor: https://wiki.civicrm.org/confluence/display/CRMDOC/Payment+Processors
Elsewhere on stackexchange, someone explains how to support other currencies https://stackoverflow.com/questions/16014643/does-authorize-net-support-different-currency-types/16031041#16031041
Could that apply to CiviCRM too ? Is it just not implemented yet ?
Somehow, we always use US$. The message above says
If you’re not sending the currency code, or if you’re using any of our other Authorize.Net APIs, no changes are required at this time. The currency code for those APIs will automatically default to the currency associated with the merchant’s processor.
What does that mean - could we change the option to euro at the merchant interface ?