Solution : https://service.sap.com/sap/support/notes/377059 (SAP Service marketplace login required)
Key words : 
sys cp    manufacturer  status  lang    frontend cp, 8600      ms        customer entry     8600the field 'language', 1610      ms        customer entry     1610thai, system-codepage        frontend-codepage   8600, th1-char language id, additional key words thai, 2-char language id, frontend code page, frontend code pages, system code page
Related Notes : 
       
| 305570 | R/3 4.6C Installation/Upgrade Thai | 
| 300872 | Control codes and CCC converter | 
| 195490 | Automatic selection of GUI frontend code page | 
| 112197 | RFC from frontend and characters that cannot be printed |