Solution : https://service.sap.com/sap/support/notes/790485 (SAP Service marketplace login required)
Key words : 
called system applies default language/code page associations, default language/code page association, language/code page list provided, system sending thai text data, produces corrupt text data, nls setting maintenance tool, language/code page configuration, kernel patch level older, solution apply kernel patch, called unicode system applies
Related Notes : 
       
| 1319517 | Unicode Collection Note | 
| 814707 | Troubleshooting for RFC connections Unicode/non-Unicode | 
| 790865 | Rfc patch collection 46 2004 | 
| 647495 | RFC for Unicode ./. non-Unicode Connections | 
| 302063 | Correspondence Language | 
| 112065 | Using customer language 'Z1' | 
| 42305 | RSCPINST (I18N configuration tool) |