Solution : https://service.sap.com/sap/support/notes/530576 (SAP Service marketplace login required)
Key words : 
install/codepage/appl_serverabap/import_conversion reason, 'abap/import_conversion' profile parameter, databse ignoring conversion errors, patch level number lower, patch level lower, national special characters, previous national characters, single code page, patch number, obvious reason
Related Notes : 
       
| 1646888 | Termin CONNE_IMPORT_CONVERSION_ERROR / IMPORT_FORMAT_ERROR | 
| 991897 | Terminatns CONNE_IMPORT_CONVERSION_ERROR/IMPORT_FORMAT_ERROR | 
| 741817 | CONNE_IMPORT_CONVERSION_ERROR during import | 
| 669195 | Profile variable abap/import_char_conversion until 6.10 | 
| 545741 | Additional information on upgrading to BW 3.1 Content | 
| 535797 | System requirements for Transaction SDCC in R/3 Rel. 6.20 | 
| 534417 | Enterprise Buyer 3.5 Server installation/upgrade Asia | 
| 532039 | SAP BW 3.0B Server installation/upgrade Asia | 
| 527047 | SAP Web AS 6.20 server installation/upgrade Asia | 
| 510835 | Additional information on upgrading to BW 3.0B | 
| 484876 | Additional information about upgrading to SAP Web AS 6.20 | 
| 144057 | abap/import_char_conversion : How to set best |