Solution : https://service.sap.com/sap/support/notes/846815 (SAP Service marketplace login required)
Key words : 
unicode system shows incorrect characters, correct future payment medium runs, system -> status -> unicode active, data medium administration, 'legacy binary mode', payment medium, unicode format, file system, payment media, transaction fdta
Related Notes : 
       
| 911190 | PMW: Entering the code page when writing and downloading | 
| 855841 | Payment medium in a Unicode system |