Solution : https://service.sap.com/sap/support/notes/672835 (SAP Service marketplace login required)
Key words : 
terms spumg unicode conversion text flag reason, /abap/docs/i18n/unicode/textflags/672835check, older releases / applications entered wrong language / textflag, spumg ambiguous language scan, single code page system, entered wrong language information, zip language field content, symptom wrong language information, entered wrong information, text flag setting
Related Notes : 
       
| 1378891 | Text flag set in error for language field in table ESTOCC | 
| 1319517 | Unicode Collection Note | 
| 1247508 | Unicode: Text indicator incorrectly set in tables | 
| 1051414 | Table EQUI, IFLOT: Incorrectly set flag 'Text Language' | 
| 963252 | Workflow: Text Language Attribute Changes (SAP internal!) | 
| 921184 | PP61: Text flag causes problems with Unicode | 
| 920552 | Missing text indicators in tables | 
| 908207 | Table T005: Problems with Unicode systems, RFC | 
| 863993 | Incorrect text flag in Table TLSY7 | 
| 826140 | Report Writer / Unicode: Text flag T800-MASTERLANG | 
| 765475 | Unicode Conversion: Troubleshooting | 
| 673941 | Unicode conversion for address tables (ADRC, ADRP) | 
| 480671 | The Text Language Flag of LANG Fields |