Solution : https://service.sap.com/sap/support/notes/928965 (SAP Service marketplace login required)
Key words : 
runtime error convt_codepageexception cx_sy_conversion_codepage, import account statement files, maintain user parameter ucp, account statement reason, special characters disappear, attached advance corrections, find detailed information, system code page, unicode code page, parameter ucp
Related Notes : 
       
| 758870 | Account statement: Character set when the file is uploaded |