Solution : https://service.sap.com/sap/support/notes/642523 (SAP Service marketplace login required)
Key words : 
-> choose options -> choose fonts tab ->choose custom settings -> enter field text = courier, select settings ->     pc editor -> sapscript tab -> deselect graphical pc editor, symptom rtl sap gui limitations / requirements / special behavior, - windows 2000 sp3 \ windows xp sp1, settings   - pc editor, 3 color pallet - alt+f12, 3 color pallet -      alt+f12, 3 color pallet-      alt+f12, tab -> choose dialog, -> choose encoding tab
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