Solution : https://service.sap.com/sap/support/notes/621613 (SAP Service marketplace login required)
Key words : 
class attribute                       attribute    type      visible    type  reference type initial, method                type   visibility            get_currency_timestmp  static  public                       parameter   type, p_c_currency  constant  private    type  rsinfoprov  '$$currency'                       create, method                type   visibility            set_currency_timestmp  static  public, optional  typing  reference type            r_timestmp  returning, 1 content            import support package 7, type        rstimestmp                       ii, 0b            import support package 13, upload exchange rates, 0b support package 13
Related Notes : 
       
| 750074 | New exchange rates are ignored | 
| 730236 | |
| 643514 | Currency upload from file: Invalidate OLAP cache | 
| 539829 | SAPBWNews BW 3.1 Content Support Package 07 | 
| 523278 | SAPBWNews BW 3.0B Support Package 13 |