Solution : https://service.sap.com/sap/support/notes/863993 (SAP Service marketplace login required)
Key words : 
terms unicode language key radntlang solution import, tlsy7-sprsl field, converting unicode, radntlang report, tlsy7-sprsl, tlsy7 table, table definition, support package, longer set, exception list
Related Notes : 
       
| 672835 | Textflags could cause problems during Unicode conversion | 
| 480671 | The Text Language Flag of LANG Fields |