Solution : https://service.sap.com/sap/support/notes/371248 (SAP Service marketplace login required)
Key words : 
sap easy access / object navigator3, thai language area menue, thai code page, billing cancellation reason, -called f1-converter, 8600  ms  customer entry  ' '  8600, gui code page 8600, control processing error, error message, errors occur
Related Notes : 
       
| 305570 | R/3 4.6C Installation/Upgrade Thai | 
| 195490 | Automatic selection of GUI frontend code page |