Hi Johan,
As SAP states, this concept is very cumbersome and difficult to implement. the other option is you create Company Codes for where you have these operations and create separate tax procedures for each country. Therefore you keep everything separate. The transactions that you deal with will be regular Inter company transactions with SD on the selling (Slovakia) for example using Slovakian tax codes and PO on the French company. Of course since they are not in SAP you have to manage all these transactions from the French company side.
Plants Abroad - Taxes (FI-AP/AR) - SAP Library
I hope it helps,
regards,
Dave