Solution : https://service.sap.com/sap/support/notes/633281 (SAP Service marketplace login required)
Key words :
left choose sap bbpcrm/sap ebp crm server 4, /xi/sus/mapping objects/message-mappings/mm2susersinvoice, mapping area expand invoiceout/invoiceheader/language 5, box labeled 'language' link, sus-mm scenario, box labeled 'en', supplier relationship management, transaction sxmb _ifr, integration server, mapping solution 1